The Imaam recited an Aayat of Sajdah in Fajr Salaat.

Answer

There is Ikhtilaaf (Difference) of our Fuqaha regarding the mas'alah of fulfilling Sajdah Tilaawat with Ruku'.

The best method is that the Imaam should not make any intention of Sajdah when going into Ruku' or when in Ruku'. His Ruku' will be an adequate substitute for the Sajdah for himself and the Muqtadis, that is if he does not make Niyyat.

However, if he does make niyyat of the Sajdah, then whilst his Sajdah will be validly discharged, the Sajdah of the Muqtadis who did not make niyyat will not be discharged.

The Muqtadis who did not make niyyat, should therefore, not join the Imaam in Salaam. When the Imaam makes Salaam, they should make the Sajdah, then sit and again recite Tashahhud, Durood Dua and complete the Salaat with Salaam as usual.

The above all apply to the Jahri Salaat. As far as the Sirri Salaat is concerned, only the Imaam has the responsibility. If he does not make Sajdah, the Muqtadis will not even know that he had recited an Aayat of Tilaawat.