Assalamualaikum,In salah, during prostation, what if I say the tasbeeh before my forehead and nose touches the ground? Sometimes mistakenly I start saying the tasbeeh before my forehead and nose touches the ground, like, when my forehead and nose are just above the ground, I say 'sub' and after touching i say 'hana rabbial ala'. Is my prayer valid in this case?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Your prayer is valid and is not invalidated by starting the Tasbeeh before having fully prostrated on the ground.

It should be noted that the Tasbeeh in prostration is a Sunnah according to the view of the majority of scholars, so the prayer is not invalidated by leaving it at all.

Allah knows best.