Ubaid bin Umair narrates that Sayyiduna Abu Musa Ash'ari (may Allah be pleased with him) went to the house of Sayyiduna Umar (may Allah be pleased with him) and sought permission to enter three times, but when permission was not granted, he turned back. Sayyiduna Umar said: Was I not just hearing the voice of Abu Musa Abdullah bin Qais? The household said: Yes, it was him. He said: Call him. So he was called. Sayyiduna Umar (may Allah be pleased with him) asked him: What made you do what you did? He said: I sought permission to enter three times, and when I was not granted permission, I turned back. This is the command we have been given. Sayyiduna Umar said: Bring proof for this, otherwise I will punish you. Sayyiduna Abu Musa went to the mosque or to the gathering of the Ansar and asked for a witness. They said: Our youngest servant will bear witness for you. So Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) stood up and bore witness for him. Sayyiduna Umar (may Allah be pleased with him) said: This Sunnah of the Messenger of Allah (peace and blessings be upon him) had remained hidden from me; the trade in the markets has made us heedless.