Rules about Performing Salah (Prayer) in an Unclean Cloth Regardless One Knows it or Not

10. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from Muhammad ibn Sinan from ibn Muskan who has said the following: “I once sent a question to abu ‘Abd Allah عليه السلام, through Ibrahim ibn Maymun and told him to ask him (the Imam) about the case of a drop of urine found on one’s thigh but one performs Salah (prayer) and then remembers that he has not washed it. He (the Imam) said, ‘He is required to perform his Salah (prayer) again.’”