Shaykh al-Islam Ibn Taymiyah said:

‘Prostration is of two types: prostration by way of pure worship, and prostration by way of honouring and greeting showing respect. As for the former, it can only be done for Allah.’

[Majmu‘ al-Fatawa (4/361)]

Prostration by way of honouring and greeting (Tahiyyah) has been abrogated with the Shari’ah of Muhammad (s):

‘This was allowed in their laws and teachings: when they greeted an elder, they would prostrate to him. This remained permissible from the time of Adam until the teachings of ‘Eesa (a), but this is prohibited for this ummah, and prostration is only for the Lord, may He be glorified and exalted.

[Tafsir al-Qur’an al-‘Azim by Ibn Kathir (4/412)]

Ibn Taymiyyah:

And he said: ‘The Muslims are unanimously agreed that prostration to anyone other than Allah is prohibited.’

[Majmu‘ al-Fatawa (4/358)]

And he said:

‘The texts of the Sunnah and the consensus of the ummah indicate that it is prohibited to prostrate to anyone other than Allah according to the law brought by our Prophet (blessings and peace of Allah be upon him), whether by way of greeting or worship, as the Prophet (blessings and peace of Allah be upon him) forbade Mu‘aadh ibn Jabal to prostrate to him when he came from Syrian and prostrated to him by way of greeting.’

[Jaami‘ al-Masaa’il (1/25)]

Imam Al-Qurtubi:

وَهَذَا السُّجُودُ الْمَنْهِيُّ عَنْهُ : قَدِ اتَّخَذَهُ جُهَّالُ الْمُتَصَوِّفَةِ عَادَةً فِي سَمَاعِهِمْ، وَعِنْدَ دُخُولِهِمْ عَلَى مَشَايِخِهِمْ وَاسْتِغْفَارِهِمْ ، فَيُرَى الْوَاحِدُ مِنْهُمْ إِذَا أَخَذَهُ الْحَالُ ـ بِزَعْمِهِ ـ يَسْجُدُ لِلْأَقْدَامِ ، لِجَهْلِهِ ؛ سَوَاءٌ أَكَانَ لِلْقِبْلَةِ أَمْ غَيْرِهَا ، جَهَالَةً مِنْهُ ، ضَلَّ سَعْيُهُمْ وَخَابَ عَمَلُهُمْ”. انتهى من “تفسير القرطبي” (1/294).

‘With regard to this prostration that is prohibited, the ignorant Sufis have taken it as a custom in their gatherings (when they begin their dhikr and nashids), and when they enter upon their Shaykhs and pray for forgiveness. So you see one of them, when he is overcome with ecstasy – as they claim – prostrating by putting his forehead to the ground, because of his ignorance, whether he is facing towards the Qiblah or otherwise, out of ignorance on his part. May they be doomed!’

[Tafsir al-Qurtubi (1/294)]

Nobody loved and venerated (without any Ghuluw) the Prophet (s) more than his companions, yet he prohibited them form prostrating to him:

Imam al-Dhahabi said:

Do you not see that the Sahaabah, in their great love for the Prophet (blessings and peace of Allah be upon him), said: Shouldn’t we prostrate to you? And he said no. If he had given them permission, they would have prostrated to him by way of honouring and showing respect, not by way of worship, as the brothers of Yoosuf (peace be upon him) prostrated to Yoosuf.

Something similar may be said about the Muslim prostrating to the grave of the Prophet (blessings and peace of Allah be upon him) by way of veneration and respect: he does not commit an act of disbelief thereby; rather he is sinning. So he should be told that this is not allowed, and the same applies to praying facing towards the grave.

End quote from Mu‘jam ash-Shuyookh al-Kabeer (1/73).

The worst of all of those who prostrate to other than Allah from among those who ascribe to Islam are the Rafidah. They not just prostrate to their saints as a form of greeting/Tahiyyah (in that case it would be a Bid’ah as this practice is completely abrogated in our Shari’ah and no Qiyas with Adam, Angel and Ya’qub will save the Rafidah) but they actually pray to them. Evidence:

1. Rafidah pray to Fatimah (a) in SUJUD invoking her for over 500 times. A Bid’ah that even Catholics haven’t concocted in the name of Mary (a).

Sunnah in Shi’ism: Prostrating and praying to Fatimah a few hundred times!

2. Shia mainstream practice: Praying to ‘Ali and Angel Jibra’il in Sujud!

Shia mainstream practice: Praying to ‘Ali and Angel Jibra’il in Sujud!