Bowing down [rukū‘] is an essential pillar of prayer. Performing it in an excessive or inadequate manner, whether intentional or unintentional, renders the prayer invalid.
The word “rak‘ah” [circle] which is used in counting the cycles of prayer is derived from the word “rukū‘”.
The tribe of Thaqīf requested that the Prophet (ṣ) excuse them from performing rukū‘ and prostration [sujūd] in prayer, saying: “Bending down for us is a shame.” This verse was revealed:
﴾ وَ إِذَا قِيلَ لَهُمُ ارْكَعُوا لا يَرْكَعُونَ ﴿
“When they are told, ‘Bow down,’ they do not bow down!”[1]
Others bow and show reverence in front of human beings like themselves, but you have to bow down and show reverence solely to your Creator.
When the verse, ﴾ فَسبِّحْ بِاسمِ رَبِّك الْعَظِيمِ ﴿ “So celebrate the Name of your Lord, the All-supreme,”[2] was revealed, the Prophet (ṣ) ordered: “Show reverence to God while you are in rukū‘ and recite this dhikr [remembrance or glorification]:
“بِحَمدهِ وَ ٱلْعَظيمِ رَبِّيَ سُبْحانَ”
Subḥāna rabbiya’l-‘aẓīm wa biḥamdih.
“Glory be to my Lord, the Great, and praise belongs to Him.”[3]
We read in the traditions: “Rukū‘ is the sign of courtesy [adab] while the sujūd is the symbol of nearness [qurb] to God. Once you do not perform the gesture of courtesy properly, you cannot be ready for the stage of nearness.”[4]
Rukū‘ is the means of repentance [tawbah], penitence and asking forgiveness in the presence of God:
﴾ فَاستَغْفَرَ رَبَّهُ وَ خَرَّ رَاكِعاً وَ أَنَاب ﴿
“Whereat he (David) pleaded with his Lord for forgiveness, and fell down bowing and repented.”[5]
