ثُمَّ يُكَبِّرُ، وَيَرْكَعُ، وَيَعْتَمِدُ بِيَدَيْهِ عَلَى رُكْبَتَيْهِ، وَيُفَرِّجُ أَصَابِعَهُ، وَيَبْسُطُ ظَهْرَهُ، وَلَا يَرْفَعُ رَأْسَهُ وَلَا يُنَكِّسُهُ، وَيَقُولُ فِي رُكُوعِهِ: «سُبْحَانَ رَبِّيَ الْعَظِيمِ» ثَلَاثًا، وَذَلِكَ أَدْنَاهُ.
Meaning: Then say the takbir and bow, place the hands on the knees, spread the fingers, level the back, keep the head neither raised nor lowered, and say “Glory be to my Lord the Magnificent” three times; this is the minimum sunnah count.
The phrase wa-dhalika adnahu concerns the minimum sunnah number of glorifications, not the minimum physical validity of bowing.