What is the ruling concerning someone who prayed an obligatory prayer, then found impurities on the clothing that he prayed with, does he repeat the prayer, may Allah reward you?
It is not binding upon you to repeat the prayer. If a person finds impurities on his clothing after having completed the prayer, he does not repeat it. Likewise is the ruling of someone who knew of the impurities but then forgot, then remembered after completing the prayer. He is not to repeat the prayer according to the correct opinion because the Messenger – عليه الصلاة والسلام – was cautioned by Jibreel (during his prayer) saying:
"There are impurities on your sandals."
So he removed them and did not repeat the first part of his prayer. This affirms that the prayer is not to be repeated if a person is unaware of the impurities or has forgotten about them, and did not become remember or become aware until the prayer was completed, the prayer is not repeated.
This is the correct opinion. If a person gives the Tasleem (Salaam at the end of the prayer) and then becomes aware that there are impurities on his clothing only after the prayer is completed, then the prayer is valid.