What is the ruling on congregational prayer behind an Imam who makes mistakes in prayer, such as not reciting aloud in audible prayers, or not completing bowing (ruku') and prostration (sujud), or mispronouncing (lahn) in Al-Fatiha, or rushing in prayer? And is it obligatory to repeat the prayer if the worshipper (ma'mum) lags behind the Imam by a pillar due to the Imam's speed?

To address the errors mentioned:

Firstly: Hearing the Imam's recitation is not a condition for the validity of following him. The congregant is permitted to recite the surah if he does not hear the Imam.

Secondly: There are two forms for bowing (Ruku'): a sufficient one and a complete one. Following the Imam is valid as long as the Imam performs the sufficient form.

Thirdly: Omitting "Sami'a Allahu liman hamidah" (Allah hears those who praise Him) does not invalidate the prayer according to the majority of scholars, as it is a Sunnah. However, according to Ahmad, it is an obligation that is compensated by the prostration of forgetfulness (sujood as-sahw) if it was omitted due to forgetfulness or ignorance.

Fourthly: The Sunnah in prostration (sujood) is to face the Qiblah with the pads of the fingers. The prayer remains valid even if one prostrates on the tops of their feet.

Fifthly: Praying in tight clothes that reveal the size of the bones is valid but disliked, as long as they do not reveal the skin color.

Sixthly: The ruling on someone who changes a letter in Al-Fatiha and the details of the validity of following him have been addressed in previous fatwas.

Seventhly: If the congregant falls behind the Imam by one pillar due to an excuse, he should perform it and then follow the Imam. However, if it is without an excuse, there is a difference of opinion. If the Imam speeds up such that following him is not possible, the congregant should separate from him and complete his prayer individually.

Eighthly: Not knowing the Imam does not prevent praying behind him, as the prayer of Muslims is valid by default. Beware of succumbing to whispers and doubts that prevent you from the virtue of congregational prayer, and do not repeat the prayer without a legal justification.