Q: Under which conditions does sajda sahu becomes wajib?
A: Sajdah Sahw is made when one or more Waajib factors in Salaah is either delayed or omitted. Every person should be acquainted with which factors are Fardh, Waajib and Sunnah in Salaah so that Sajdah Sahw will be made for the right reasons. Sajdah Sahw cannot compensate for a defect in a Fardh factor of Salaah nor is Sajdah Sahw necessary for leaving out a Sunnah of Salaah.