The students in some schools stand up, clasp their hands and repeat the words “O our Father we thank you for the night…” What is the ruling on that?

Firstly: 

The Messenger of Allah (blessings and peace of Allah be upon
him,) who is the most truthful one, told us that this ummah would follow the
ways of the Jews and Christians. It was narrated from Abu Sa ‘eed (may Allah
be pleased with him) that the Prophet (blessings and peace of Allah be upon
him) said: “You will certainly follow the ways of those who came before you
hand span by hand span, cubit by cubit, to the extent that if they entered
the hole of a lizard, you will enter it too.” We said: “O Messenger of
Allah, (do you mean) the Jews and the Christians?” He said: “Who else?”
Narrated by al-Bukhaari, 1397; Muslim, 4822. 

This hadeeth indicates that it is haraam to imitate the Jews
and the Christians, and that those who follow them and tread the same path
as them are criticized. Islam has reinforced this prohibition, by describing
those who imitate the kuffaar as being of them.  

It was narrated that ‘Abdullah ibn ‘Umar (may Allah be
pleased with him) said: The Prophet (peace and blessings of Allah be upon
him) said: “Whoever imitates a people is one of them.” Narrated by Abu
Dawood, 3512; classed as saheeh by al-Albaani in Irwa’ al-Ghaleel,
2691.  

Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him)
said: 

This at the very least indicates that it is haraam to imitate
them, although the apparent meaning is that the one who imitates them is a
kaafir. 

Iqtida’ al-Siraat al-Mustaqeem,
237. 

The phrase asked about here (“O our Father we thank you for
the night…”) Is most likely to be a Jewish or Christian prayer, because they
are the ones who describe God, may He be glorified, as their Father, exalted
be Allah above what they say. Indeed Allah, may He be glorified, and His
Angels and His Messengers have nothing to do with them or their disbelief.
This is confirmed in the Qur’an where Allah, may He be exalted, says
(interpretation of the meaning):

“And (both) the Jews and the Christians say: ‘We are the
children of Allah and His loved ones.’ Say: ‘Why then does He punish you for
your sins?’ Nay, you are but human beings, of those He has created, He
forgives whom He wills and He punishes whom He wills. And to Allah belongs
the dominion of the heavens and the earth and all that is between them, and
to Him is the return (of all)”

[al-Maa’idah 5:18]. 

In fatwa no. 160791 we stated that it is not permissible to
address Allah, may He be glorified and exalted, by saying “O my Father” or
“O our Father”; these are the words of the people of the two previous Books,
the Jews and Christians. 

Based on that, it is not permissible to use this phrase in
supplication (du‘aa’). 

Secondly: 

With regard to the question about using this phrase in the
prayer “O Allah, we thank you for the night…”, this, by Allah, is something
strange and is indicative of how far this ummah has sunk into humiliation,
feelings of inferiority and backwardness, and defeatist thinking. Hence it
hastens to imitate the disbelievers even in their prayers and religious
rituals. It is absolutely astounding that anyone would forsake the Qur’anic
du‘aas that are from the words of the Lord of the Worlds, may He be
glorified and exalted, and would forsake the Prophet’s du‘aa’s, and the
adhkaar of the morning and evening which are the words of the best of
mankind, then hasten to use the prayers of the disbelievers after
introducing some modifications and improvements to them. 

One may say that there is nothing wrong or objectionable in
saying “O Allah, we thank You for the night” in and of itself, for morning
and evening (or day and night) are among the blessings that Allah has
bestowed upon His slaves, for which they should give thanks, as Allah, may
He be exalted, says (interpretation of the meaning):

“Say (O Muhammad (blessings and peace of Allah be upon him)):
‘Tell me! If Allah made day continuous for you till the Day of Resurrection,
who is an ilah (a god) besides Allah who could bring you night wherein you
rest? Will you not then see?’

It is out of His Mercy that He has put for you night and day,
that you may rest therein (i.e. during the night) and that you may seek of
His Bounty (i.e. during the day), and in order that you may be grateful”

[al-Qasas 28:72-73].

But if the one who says that is bearing in mind what the
disbelievers say and paying attention to their wording in their
supplication, then this undoubtedly comes under the heading of imitation of
the disbelievers which is prohibited, especially when it has to do with a
matter of worship and remembering Allah, may He be exalted. 

Therefore it is haraam to stick to such wording and to choose
it deliberately, in this regard. 

Moreover, the matter becomes even more emphatically
prohibited, and the one who does it definitely falls into the category of
imitation of the disbelievers which is prohibited, if that is accompanied by
clasping the hands in the manner mentioned, as the disbelievers, Hindus and
others, do in their prayers and worship. 

For more information, please see the answer to question
no.
21341 

And Allah knows best.