Is the prayer of one who doubts their recitation of "Muhammad is His servant and messenger" and repeats it without repeating the Tashahhud from the beginning invalidated? And is "salli" (send blessings) written with or without a yaa' (ي)? And is "Muhammadun" (Muhammad, nominative) or "Muhammadan" (Muhammad, accusative) used in the Tashahhud? And is the prayer of one who sometimes pronounces it "Muhammadun" and sometimes "Muhammadan" invalidated?

The continuity (muwalat) between the words of the tashahhud is obligatory according to some jurists. If someone forgets an obligatory word in the tashahhud and then remembers it before the salam, with a short interval, they should pronounce the forgotten word and what follows it, and are not required to recite the tashahhud from the beginning. Their prayer is valid. The word "salli" (صَلِّ) is pronounced without the 'ya' because it is a vocative verb in the imperative form, and "Muhammadan" (محمدًا) is pronounced with the 'alif' because it is the اسم "أن" (ism of 'anna').