When in Doubt about the Number of Rakaahs Performed

Q: Salaah-139: An lmaam is in doubt about whether he had performed the first or the second Rakaah. He therefore pays attention to whether the followers will be standing up for another Rakaah when he calls out the Takbeer, so that he would know which Rakaah it is. Will the salaah be valid if the Imaam employs this method of correcting himself?

Answer: The salaah will be valid and there is no need for Sajdah Sahw or for repeating the salaah. And Allaah knows best what is most correct.

Fatawa Rahimiyyah vol.2