Jami` at-Tirmidhi 396

جامع الترمذي#396Sahih

Iyad bin Hilal said:"I said to Abu Sa'eed: 'One of us performs Salat and we do not know how (much) we prayed.' So he said: 'Allah's Messenger (S) said: "When one of you performs Salat and he does now know how (much) he prayed then let him perform two prostrations while he is sitting

Scholarly Authentication

We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:

Ahmad Muhammad ShakirSahih

Al-AlbaniSahih

Bashar Awad MaaroufHasan

Zubair Ali ZaiIsnaad Hasan

In-book reference: 2:249

All of Jami` at-Tirmidhi