Is prayer invalidated behind an imam who pronounces "Al-Sirat" with a "sad" (ص) or who pronounces the "lam" in "Al-Dalleen" without tashdeed (emphasis)?

If someone replaces a letter with another in Al-Fatiha, while being able to correct it, their prayer is invalid. This is except for replacing the letter Dhad (ض) with Zha (ظ), or the letter Sad (ص) with Seen (س) or Zay (ز) in "As-Sirat" (الصراط), due to the existence of recitations with these variations. If they are unable to correct it, their prayer is valid, but they should only lead others who are similar to them.

Similarly, if someone omits a letter or a shaddah (doubling) from Al-Fatiha, their prayer is invalid, unless they are unable to correct it.

It is obligatory to advise the Imam to correct his recitation, or to refrain from leading the prayer if he is unable to do so.