Al-Matalib al-'Aliyah 386 — What is to be avoided in prayer

It is narrated from Alqamah bin Qays (although the narrator's hearing from Alqamah is not established) that Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) came to the house of Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him), and the time of prayer arrived. Sayyiduna Abu Musa (may Allah be pleased with him) said (out of respect for him): "O Abu Abd al-Rahman! Step forward to lead the prayer, for you are older than me in age and superior to me in knowledge as well." Sayyiduna Abdullah (may Allah be pleased with him) said: "No, rather you step forward, for we have come to you in your house and your mosque (place of prayer), so you are more entitled to lead." So Sayyiduna Abu Musa (may Allah be pleased with him) stepped forward and took off his shoes (for the prayer). When he finished with the salam, Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) asked him (by way of question): "What did you intend by taking them off? Are you in the sacred valley of Tuwa [Surah Ta Ha: 12]?"
This narration is munqati' (broken), because Abu Ishaq's hearing from Alqamah bin Qays is not established.