In rukū' the sunnah is to say "Subḥāna Rabbiya'l-'Aẓīm" (Glory to my Lord the Most Great), and in sujūd "Subḥāna Rabbiya'l-A'lā" (Glory to my Lord the Most High), as Ḥudhayfah reported the Prophet (ﷺ) saying in his night prayer. Saying it three times is recommended, and it may be repeated more. Prostration is especially a place for supplication, for the Prophet (ﷺ) said, "The closest a servant is to his Lord is when he is prostrating, so make much supplication," so one may add du'ā of his own after the tasbīḥ, in the obligatory prayers keeping to what is reported.
Evidence — the daleel
Sahih Muslim 772 ṢaḥīḥSahih Muslim 482 Ṣaḥīḥ
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.