Is prayer valid behind an Imam who has a lot of dirt in the cracks of his feet, knowing that he is ignorant of the ruling?

What prevents water from reaching the skin must be removed. However, slight dirt under the fingernails and in the cracks of the feet, and what is difficult to remove, is excused. This is what some scholars, such as Ibn Taymiyyah, chose, by analogy with the dirt under the fingernail. Therefore, the dirt in the cracks of the feet is excused, and prayer behind the Imam is valid.