Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) led the prayer and took off his sandals during the prayer, and the people also took off their sandals. When he (peace and blessings be upon him) finished, he asked: "Why did you take off your sandals?" They said: "O Messenger of Allah, we saw you take off your sandals, so we took ours off too." He (peace and blessings be upon him) said: "Jibril came to me and informed me that there was filth on them. So when one of you comes to the mosque, let him turn his sandals over and look; if there is filth on them, let him wipe them on the ground and then pray in them." This hadith is sahih (authentic) on the condition of Muslim, but the two Shaykhs did not record it.