Should he pray behind someone whose ‘aqeedah is not known, whether there are Sufis and Shi’as in the country?

Praying in congregation is obligatory for the one who can
hear the call. If your house is so far away from the mosque that you cannot
hear the adhaan if the muezzin raises his voice without the aid of a
loudspeaker, when the wind and other noises etc. that could affect your
hearing it are silent, then you are not obliged to attend congregational
prayers in the mosque. 

We have already discussed this in the answers to questions
no. 21969 and
20655. 

With regard to Jumu’ah prayer, the scholars are unanimously
agreed that it is obligatory for every man who is in the city, whether he
can hear the call or not, and no matter how far apart the city limits are. 

For more information, see the answer to question no.
39054 

Secondly: 

So long as the imam is outwardly a Muslim, it is not
permissible to abandon Jumu’ah and prayer in congregation behind him because
of the possibility that he may be a Shi’ah or a Sufi, unless it is possible
to establish another congregation for praying Jumu’ah and prayers in
jamaa’ah – without causing any fitnah – behind another imam who is known to
be righteous and following a sound way, in which case it is better to pray
behind that one. 

The basic principle is that we should think positively of
Muslims, and not impugn their religious commitment or path without proof.
The correct view is that it is valid to pray behind anyone whom we regard as
a Muslim, so long as he does not do anything that constitutes kufr, such as
believing that the Qur’aan has been altered or regarding the companions of
the Prophet (peace and blessings of Allaah be upon him) as kaafirs, or
praying to the dead and seeking their help. We should not pray behind one
who does such things. 

Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him)
was asked about praying behind al-muraaziqah and about their bid’ah. 

He replied: It is permissible for a man to offer the five
daily prayers and Jumu’ah etc behind a person whom he does not know to
engage in bid’ah or evildoing, according to the consensus of the four Imams
and other imams of the Muslims. It is not one of the conditions of leading
prayers that the person praying behind the imam should know what his imam’s
beliefs are, and he should not examine him by saying, “What do you believe?”
Rather he should pray behind the one whose situation he does not know. If he
prays behind one who he knows to be an evildoer or innovator, then there are
two well-known scholarly views concerning the validity of his prayer in the
madhhab of Ahmad and Maalik; the view of al-Shaafa’i and Abu Haneefah is
that his prayer is valid. 

If the person knows that the imam is an innovator who calls
others to follow his bid’ah, or an evildoer who commits evil openly, and he
is the regular imam and it is not possible to pray behind anyone else, such
as the imam for Jumu’ah and Eid prayers, or the imam in Hajj prayers at
‘Arafah and so on, then he should pray behind him, according to the majority
of earlier and later scholars. This is the view of Ahmad, al-Shaafa’i, Abu
Haneefah and others. 

Hence they said concerning ‘aqeedah: He should offer Jumu’ah
and Eid prayers behind any imam, whether he is righteous or an evildoer.
Similarly, if there is only one imam in a village, then the prayers in
congregation should be offered behind him, because praying in congregation
is better than praying alone, even if the imam is an evildoer. This is the
view of the majority of scholars, Ahmad ibn Hanbal, al-Shaafa’i and others.
Prayer in congregation is obligatory for individuals according to the view
of Ahmad. Whoever abandons Jumu’ah prayer and prayer in congregation behind
an imam who is an evildoer is an innovator according to Imam Ahmad and other
imams of al-Sunnah. 

The correct view is that he should pray and not repeat the
prayers. The Sahaabah used to offer Jumu’ah prayers and prayers in
congregation behind imams who were evildoers, and they did not repeat the
prayers. Ibn ‘Umar used to pray behind al-Hajjaaj, and Ibn Mas’ood and
others prayed behind al-Waleed ibn ‘Uqbah, who used to drink wine. The
prayer of an evildoer or innovator is valid in and of itself, so if a person
prays behind him, his prayer is not invalid.  

But with regard to those who disliked the idea of praying
behind one who is an evildoer, they based their view on the fact that
enjoining what is good and forbidding what is evil is obligatory. So one who
openly commits bid’ah or evil should not be appointed as the regular imam
for the Muslims. He deserves to be rebuked until he repents, and if it is
possible to shun him until he repents, then that is good. If some of the
people stop praying behind him and pray behind someone else, that may affect
him and make him repent or withdraw or make the people stop committing sins
like his. Stopping praying behind such a man may serve a purpose so long as
people do not miss out on praying Jumu’ah or other prayers in congregation.
But if stopping praying behind him means that people will miss out on
praying Jumu’ah or other prayers in congregation, then in this case no one
will stop praying behind him but one who is an innovator and who goes
against the Sahaabah (may Allaah be pleased with them).

 End quote from Majmoo’ al-Fataawa, 23/351- 356 

The scholars of the Standing Committee were asked: What is
the ruling on eating meat when nothing is known about the slaughterer’s
‘aqeedah, or praying behind one whose ‘aqeedah is unknown? They replied: If
he is outwardly Muslim, but his ‘aqeedah is unknown, and it is not known
whether his ‘aqeedah is deviant, then it is valid to pray behind him and
meat slaughtered by him may be eaten. End quote. 

Fataawa al-Lajnah al-Daa’imah,
7/365 

It also says (7/353):
With regard to praying behind an innovator, if their bid’ah involves shirk
such as calling upon anyone other than Allaah, making vows to anyone other
than Allaah, or believing that their shaykhs possess qualities that belong
only to Allaah, such as complete knowledge or knowledge of the unseen or the
ability to influence events, then it is not valid to pray behind them. 

But if their bid’ah does not involve shirk, such as reciting
dhikrs that have been narrated from the Prophet (peace and blessings of
Allaah be upon him) but in unison and swaying, then it is valid to pray
behind them, but the Muslim should try to find an imam who does not follow
innovation, because that will bring a greater reward and be further removed
from evil. End quote. 

Shaykh Ibn Baaz (may Allaah have mercy on him) was asked:
What is the ruling on one who lives in a city whose people adhere to bid’ah?
Is it valid for him to offer Jumu’ah and prayers in congregation with him,
or should he pray on his own, or is the obligation of Jumu’ah waived for
him? If there are less than twelve of ahl al-sunnah in a city, is Jumu’ah
valid for them or not? 

He replied: It is obligatory to establish Jumu’ah prayer
behind any imam, righteous or otherwise. If the bid’ah of the imam for
Jumu’ah does not put him beyond the pale of Islam, then he should pray
behind him. Imam Abu Ja’far al-Tahhaawi (may Allaah have mercy on him) said
in his famous book al-‘Aqeedah: We think that prayer should be
offered behind any imam, righteous or otherwise, among the people of the
qiblah, and (the funeral prayer) should be offered for those of them who
die. End quote. Then he quoted the words of the former Shaykh of Islam: … as
for the second question, the answer is: There is a well-known dispute among
the scholars concerning this issue, but the correct view is that it is
permissible to establish Jumu’ah prayer with three or more, if they are
residents of a village in which Jumu’ah prayers are not held. As for the
stipulation that there be forty or twelve or less or more in order to hold
Jumu’ah prayers, there is no reliable evidence for that as far as we know.
Rather what must be done is to establish prayers in congregation and the
smallest number for that is three. This is the view of a number of scholars,
and is the view favoured by Shaykh al-Islam Ibn Taymiyah (may Allaah have
mercy on him), and this is the correct view, as stated above. 

End quote from Majmoo’ Fataawa al-Shaykh Ibn Baaz,
4/303 

You should cooperate
with the community that is in that land, and call them to Allaah, and
correct their ‘aqeedah, teaching those who have gone astray, with wisdom and
beautiful preaching, so that the prayers will be led by the best and most
pious of them.

 We ask Allaah to help and guide us and you. 

And Allaah knows best.