Subhanallah once in ruku or sujuud
In the name of Allah, the most Beneficent, the most Merciful.
It is mustuhub to say Subhanallah Rabbi Yal Azeem three times in ruku and Subhana Rabbi Yal Aala three times in sujuud (prostration). To say it less than that is slightly disliked. (Makruh Tanzihi). (Ruddul Muhtar p.197 v.2)
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham