If the Imam is Unsure whether or not there is some Filth on His Garment
Question :
If the Imam is unsure whether or not there is some filth on his garment, but he did not leave the prayer because it was merely a doubt, then after the prayer, he found that there was some filth on his clothes - what is the ruling? And should he leave the prayer in a similar situation, simply due to a doubt, or wait until he has prayed?
Answer:
If a worshipper is in doubt over the presence of filth on his clothes while he is praying, it is not permissible for him to leave the prayer, whether he be the Imam, or one being led in prayer or praying alone.
He must complete his prayer, and if he finds after that, that there is some filth on his clothing, he is not obliged to make up for it, according to the most authoritative of two opinions held by the scholars. This is because he was not certain until after the prayer that it was there. It has been authentically reported from the Prophet that he removed his shoes while praying, when Jibril, peace be upon him, informed him that there was some filth on them; and he did not repeat the first part of the prayer, rather, he continued his prayer. And Allah is the Granter of success.
Source:
Ibn Baz
Fatawa Islamiyah, Vol. 2 Pages 161-162