All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Bowing while greeting is forbidden for the Hadeeth reported by At-Tirmithi that a person asked the Prophet about bowing while greeting, and he answered in the negative.
Bowing is similar to Rukoo’ (bowing down in prayer). So, Rukoo’ and Sujood (prostration) are reserved for Allah Alone in Islamic Sharee’ah.
As for making Du'aa’ (supplicating) at the grave of a Wali (pious person) or visiting it to make Du'aa’, then this is among the innovations. Imam Ibn Taymiyyah said: “Visiting the grave to beg from the buried person or to ask him to make Du'aa’ or intercession for the visitor or to make Du'aa’ at that place believing that the supplications are responded to there, then all these deeds are among the innovations that are not proved from the Prophet Muhammad or from his Companions. The Companions never visited the grave of the Prophet Mohammad or other graves to supplicate Allah. Indeed, it is a sort and means of Shirk.”
The evidence is the sayings of Allah (which mean):
• {And [He revealed] that the masjids are for Allah, so do not invoke with Allah anyone.} [Quran 72:18]
• {And do not invoke besides Allah that which neither benefits you nor harms you, for if you did, then indeed you would be of the wrongdoers.'"} [Quran 10:106]
There are many other verses that prohibit calling other than Allah. The Prophet said: “When you ask, you should ask Allah, and when you seek help, you should seek it from Allah Alone” [At-Tirmithi]
The Prophet used to take from his Companions the oath of pledge that they should not ask from people. There is no proof that any one of the Companions ever visited the grave of the Prophet Mohammad or any other grave to make Du'aa’, let alone the matter of asking from the buried even though they face many calamities and trials.
Therefore, the Companions' practice proves that asking Du'aa’ from a buried person or asking blessings through a grave is not permitted.
Allah knows best.