Bowing to anyone other than Allaah is haraam
Answer
Praise be to Allaah.
The usual greeting is “Assalaamu ‘alaykum wa rahmat-Allaahi wa barakaatuhu (Peace be upon you, and the Mercy of Allaah and His Blessings), because Allaah says (interpretation of the meaning):
“greet one another with a greeting from Allaah (i.e. say: As-Salaamu ‘Alaykum — peace be on you), blessed and good”
[al-Noor 24:61]
The ahaadeeth explain this greeting clearly.
But bowing is not permitted, unless the person being greeted is old and is unable to stand up, or is one of your parents and you do not want to make him or her stand up to shake your hand or embrace you. So if you bow and kiss his head or forehead out of respect for the rights that he has over you, then this is not the kind of bowing that constitutes an act of worship. Undoubtedly bowing is an act of worship towards Allaah, as in rukoo’ (the bowing in prayer), so if that is done without shaking hands or kissing, it is an act of veneration towards that person and is therefore shirk.