Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) was once praying with his companions when he suddenly took off his sandals and placed them to his left. When the companions saw this, they also took off their sandals. When the Prophet (peace and blessings be upon him) finished the prayer, he said: "What made you take off your sandals?" They replied: "We saw you take off your sandals, so we also took ours off." The Prophet (peace and blessings be upon him) said: "Jibril (peace be upon him) came to me," or he said: "Jibril (peace be upon him) came and informed me that there was impurity on my sandals (so I took them off). Therefore, when any of you comes to the mosque, he should turn his sandals over and look at them. If he sees any impurity or filth on them, he should remove it, and then he may pray wearing them."