Does prayer become invalid if underwear is slightly stained with stool from the anus?

The purity of one's garment from impurity is a condition for the validity of prayer, as Allah Almighty says: "And your garments purify." Whoever prays in an impure garment, his prayer is not valid. As for someone from whom impurity continuously or mostly exits, and it is difficult for him to wash it, he takes the ruling of a person with incontinence; he should take precautions and perform ablution for each prayer, and his prayer will be valid.