Removing the sandals during prayer

It is narrated from Sayyiduna Anas (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) never took off his shoes during prayer except once. When he (peace and blessings be upon him) took off his shoes, the people also took theirs off. He (peace and blessings be upon him) asked: "What is the matter with you (why did you take off your shoes)?" They said: You took yours off, so we took ours off. He (peace and blessings be upon him) said: "Jibril (peace be upon him) informed me that there was filth (or something harmful) on them."
This hadith is sahih (authentic) on the condition of Imam Bukhari, since he used Abdullah bin al-Muthanna as evidence, but the two Shaykhs did not record it. Its supporting narration (shahid) is the well-known hadith of Maymun al-A'war.

It is narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) took off his sandals during the prayer, so the people behind him also took off their sandals. He (peace and blessings be upon him) asked: "What made you take off your sandals?" They said: "We saw you take them off, so we took ours off too." He (peace and blessings be upon him) said: "Indeed, Jibril informed me that there was filth on one of them, so I took them off for that reason. So do not take off your sandals (without cause)."