Musnad Ahmad 26:846

Hassan ibn Musa narrated to us, Zuhayr narrated to us, from Abu Ishaq, from Alqama ibn Qays—and he did not hear it from him, and a man asked him about the hadith of Alqama, and it is this hadith—that Abdullah ibn Mas’ud came to Abu Musa al-Ash’ari in his house. The time for prayer arrived, and Abu Musa said, "Step forward, O Abu Abd al-Rahman, for you are older in age and more knowledgeable." He said, "No, rather you step forward, for we have come to you in your house and your mosque, so you are more entitled." He said, so Abu Musa stepped forward and took off his sandals. When he finished the prayer, he said, "What did you intend by taking them off? Are you in the Sacred Valley? I have seen the Messenger of Allah, peace and blessings of Allah be upon him, praying in leather socks and sandals."