Is it permissible for a Muslim to exercise ijtihad (independent reasoning) in matters concerning prayer or purification whose legal ruling he is unaware of, and then later ask the Imam? And must he repeat the prayers he performed based on his ijtihad if they contradict the Imam's fatwa, or is it sufficient for him to repeat only the prayer specifically addressed by the fatwa?

Prayer is the second pillar of Islam, and an accountable Muslim must learn its rulings for their prayer to be valid, as well as the rulings on purification related to it. Whoever does not know Allah’s ruling on acts of worship is not permitted to perform them; they must learn or ask scholars. If the doubtful matters in purification and prayer are such that prayer is not valid without them, and they were not performed correctly, then the prayer is invalid and must be made up. This can be known by asking people of knowledge or by consulting books of Fiqh.

If the invalidity of a prayer becomes clear due to an error in purification or prayer, only the prayer in which the error occurred should be repeated. It is not a condition for the worshiper to have detailed knowledge of prayer rulings if they perform it in a way that suffices; the criterion is validity, not detailed knowledge. In case of doubt and the absence of someone to ask, a Muslim should perform purification and prayer in the manner known among the general Muslim populace, then ask people of knowledge later. If informed of its invalidity, they should repeat it; otherwise, not. Ijtihad (definition) (independent reasoning) is not permissible except for those who are well-versed in Fiqh.