Prostrating to the Prophet (peace and blessings of Allah be upon him) constitutes disbelief in Allah (kufr)

Firstly, one of the things that are well known in Islam and
that no Muslim has any excuse for not knowing is that it is not permissible
to do any kind of act of worship for anyone except Allah – not to any angel
who is close to Him or to any Prophet who was sent. Whoever does any kind of
act of worship for anyone other than Allah is a mushrik (polytheist, one who
associates others with Allah) and a kaafir (disbeliever). The evidence for
that is the verse in which Allah says (interpretation of the meaning): 

“And the mosques are for Allah (Alone), so invoke not anyone
along with Allah”
[al-Jinn 72:18]. 

Ibn Katheer said: Here Allah is commanding His slaves to
worship Him alone and not to call on anyone alongside Him, and not to
associate anyone with Him. 

This action is a kind of exaggeration about the Messenger of
Allah (peace and blessings of Allah be upon him), which the Prophet (peace
and blessings of Allah be upon him) warned us against and forbade us to do.
He said: “Do not exaggerate about me as the Christians exaggerated about the
son of Maryam, for I am no more than His slave, so say, the slave of Allah
and His Messenger.” Undoubtedly this action (prostrating) is a form of
worship.

(Narrated by al-Bukhaari, Ahaadeeth al-Anbiya’,
3189). 

Undoubtedly this action is a kind of worship, and the Prophet
(peace and blessings of Allah be upon him) warned us against following the
Jews and Christians in that. He said during his final illness: “May the
curse of Allah be upon the Jews and Christians, for they took the graves of
their Prophets as places of worship.” He was warning against doing what they
did. (Narrated by al-Bukhaari, al-Salaah, 417)

And the Prophet (peace and blessings of Allah be upon him)
warned us against standing up for him. It says in the hadeeth [referring to
when he led them in prayer sitting down because he was ill, and they were
standing, so he gestured to them to sit down]: “Just now you nearly did the
action of the Persians and Romans, who stand up for their kings whilst they
[the kings] are sitting.” (Narrated by Muslim, al-Salaah, 624) 

And it says in the hadeeth: “Do not do as the Persians do for
their leaders.” This is narrated in Saheeh al-Jaami’, 7380. If this
is what is said about standing up for him (peace and blessings of Allah be
upon him), then what about prostrating for him? 

Prostration in this manner is one of the most exclusive acts
of worship, to be done only for Allah, may He be glorified and exalted.
Allah has commanded us to prostrate to Him alone and none other, as He says
(interpretation of the meaning): 

“Prostrate yourselves not to the sun nor to the moon, but
prostrate yourselves to Allah Who created them, if you (really) worship Him”

[Fussilat 41:37] 

“So fall you down in prostration to Allah and worship Him
(Alone)”

[al-Najm 53:62]. 

For more information on the issue of prostration to anyone or
anything other than Allah, please see the answer to question no.
229780.

Secondly: what is prescribed in Islam is to send blessings
upon the Prophet (peace and blessings of Allah be upon him) when making
du‘aa’. This is a kind of etiquette to which attention should be paid. 

Al-Nawawi said: The scholars are unanimously agreed that it
is mustahabb to begin du’aa’ with praise of Allah, then to send blessings
upon the Messenger of Allah (peace and blessings of Allah be upon him), and
to conclude the du’aa’ in like manner, as it says in the hadeeth: 

“Whilst the Messenger of Allah (peace and blessings of Allah
be upon him) was sitting, a man entered and prayed, then he said, ‘O Allah,
forgive me and have mercy on me.’ The Messenger of Allah (peace and
blessings of Allah be upon him) said, ‘You are in a hurry, O worshipper.
When you have prayed, sit and praise Allah as He deserves to be praised,
then send blessings upon me, and then call upon Him (make du‘aa’).’ Then
another man prayed and then praised Allah and sent blessings upon the
Prophet (peace and blessings of Allah be upon him). The Prophet (peace and
blessings of Allah be upon him) said, ‘O worshipper, make du‘aa’, for you
will be answered.’” 

(Narrated by al-Tirmidhi, al-Da’waat, 3398; Abu Dawood,
1481; classed as saheeh by al-Albaani in Saheeh Abi Dawood, no.
2756). 

It was narrated that Faddaalah ibn ‘Ubayd said: “The Prophet
(peace and blessings of Allah be upon him) heard a man making du‘aa’ during
his prayer, but he did not send blessings upon the Prophet (peace and
blessings of Allah be upon him). The Prophet (peace and blessings of Allah
be upon him) said: ‘This man is in a hurry.’ Then he called him and said to
him, or to someone else, ‘When any one of you prays, let him begin by
praising Allah, then let him send blessings upon the Prophet (peace and
blessings of Allah be upon him), then after that let him make du’aa’ as he
wishes.’” Abu ‘Eesa said: this is a saheeh hasan hadeeth. (al-Tirmidhi,
3399; classed as saheeh by al-Albaani in Saheeh Abi Dawood, 2767) 

It was narrated in a hadeeth that ‘Abd-Allah ibn Mas’ood
said: “I was praying, and the Prophet (peace and blessings of Allah be upon
him) was nearby, and Abu Bakr and ‘Umar were with him. When I sat I started
by praising Allah, then I sent blessings upon the Prophet (peace and
blessings of Allah be upon him), then I prayed (made du‘aa’) for myself. The
Prophet (peace and blessings of Allah be upon him) said, ‘Ask, it will be
given to you; ask, it will be given to you.’” (Narrated by al-Tirmidhi, al-Jumu’ah,
541; al-Albaani said in Saheeh al-Tirmidhi, it is hasan saheeh; no.
486). 

If it is asked, how do we send blessings upon the Prophet
(peace and blessings of Allah be upon him)? 

The answer is: 

The way to send blessings upon the Prophet (peace and
blessings of Allah be upon him) is to say: “Allahumma salli ‘ala Muhammad
wa ‘ala aali Muhammad kamaa salayta ‘ala aali Ibraaheem. Wa baarik ‘ala
Muhammad wa ‘ala aali Muhammad kama baarakta ‘ala aali Ibraaheem
fi’l-‘aalameen innaka hameedun majeed (O Allah, send blessings upon
Muhammad and upon the family of Muhammad, as You sent blessings upon the
family of Ibraaheem, and bless Muhammad and the family of Muhammad, as You
blessed the family of Ibraheem among the nations. Verily You are Most
Praiseworthy, Full of Glory).”

(Narrated by al-Bukhaari, Ahaadeeth al-Anbiya’, 3119) 

This is how blessings are sent upon the Prophet (peace and
blessings of Allah be upon him). As for what is mentioned in the question
about prostrating for the Prophet (peace and blessings of Allah be upon
him), this is haraam (forbidden) and is major shirk, because
prostration may only be done for Allah. So the Muslim must learn about the
matters of his religion from the Qur’aan and Sunnah and from trustworthy
scholars; he should ask about everything that he does not understand, so
that he will not fall into shirk, Allah forbid.

He should also keep away from everyone who enjoins shirk,
bid’ah (innovation) and misguidance. We ask Allah to keep us safe and sound.

And Allah knows best. 

May Allah send blessings upon our Prophet Muhammad.