What should I do if I make mistakes in prayer, such as erring in the adhkar (remembrances) or reciting only Al-Fatihah during ruku' (bowing), or forgetting the taslim (salutation of peace) in congregational or individual prayer?

Errors in prayer do not have a single ruling; each error has its own ruling. For one who says "Allahu Akbar" instead of "Sami'a Allahu liman hamidah," there is a specific ruling. Reciting Al-Fatiha in bowing (rukūʿ) is incorrect; what is prescribed is to say "Subhana Rabbi al-ʿAẓīm." Reciting more than Al-Fatiha while standing (qiyām) is recommended by the majority of scholars. If one forgets the salutation (taslīm) and remembers it shortly thereafter, he should give the salutation and perform the prostration of forgetfulness (sujūd as-sahw). If a long time passes, his prayer becomes null and void, and he must repeat it.