While I was present in one of the gatherings of the Ansar, Abu Musa came as if he was scared, and said, "I asked permission to enter upon ʿUmar three times, but I was not given the permission, so I returned." (When ʿUmar came to know about it) he said to Abu Musa, "Why did you not enter?'. Abu Musa replied, "I asked permission three times, and I was not given it, so I returned, for Messenger of Allah ﷺ said, "If anyone of you asks the permission to enter thrice, and the permission is not given, then he should return.' " ʿUmar said, "By Allah! We will ask Abu Musa to bring witnesses for it." (Abu Musa went to a gathering of the Ansar and said). "Did anyone of you hear this from the Prophet ﷺ ?" Ubai bin Kaʿb said, "By Allah, none will go with you but the youngest of the people (as a witness)." (Abu Saʿid) was the youngest of them, so I went with Abu Musa and informed ʿUmar that the Prophet ﷺ had said so. (See Hadith No. 277, Vol. 3)  

كُنْتُ فِي مَجْلِسٍ مِنْ مَجَالِسِ الأَنْصَارِ إِذْ جَاءَ أَبُو مُوسَى كَأَنَّهُ مَذْعُورٌ فَقَالَ اسْتَأْذَنْتُ عَلَى عُمَرَ ثَلاَثًا فَلَمْ يُؤْذَنْ لِي فَرَجَعْتُ فَقَالَ مَا مَنَعَكَ قُلْتُ اسْتَأْذَنْتُ ثَلاَثًا فَلَمْ يُؤْذَنْ لِي فَرَجَعْتُ وَقَالَ رَسُولُ اللَّهِ ﷺ إِذَا اسْتَأْذَنَ أَحَدُكُمْ ثَلاَثًا فَلَمْ يُؤْذَنْ لَهُ فَلْيَرْجِعْ فَقَالَ وَاللَّهِ لَتُقِيمَنَّ عَلَيْهِ بِبَيِّنَةٍ أَمِنْكُمْ أَحَدٌ سَمِعَهُ مِنَ النَّبِيِّ ﷺ فَقَالَ أُبَىُّ بْنُ كَعْبٍ وَاللَّهِ لاَ يَقُومُ مَعَكَ إِلاَّ أَصْغَرُ الْقَوْمِ فَكُنْتُ أَصْغَرَ الْقَوْمِ فَقُمْتُ مَعَهُ فَأَخْبَرْتُ عُمَرَ أَنَّ النَّبِيَّ ﷺ قَالَ ذَلِكَ وَقَالَ ابْنُ الْمُبَارَكِ أَخْبَرَنِي ابْنُ عُيَيْنَةَ حَدَّثَنِي يَزِيدُ عَنْ بُسْرٍ سَمِعْتُ أَبَا سَعِيدٍ بِهَذَا  

I was sitting in one of the meeting of the Ansar. Abu Musa came terrified. We asked him; what makes you terrified? He replied: ‘Umar sent for me; so I went to him and asked his permission three times, but he did not permit me (to enter), so I came back. He asked; what has prevented you from coming to me? I replied: I came and asked permission three times, but it was not granted to me (so I returned). The Messenger of Allah (May peace be upon him) has said: When one of you asks permission three times and it is not granted to him, he should go away. He (‘Umar’) said; establish the proof of it. So Abu Sa’id said: the youngest of the people will accompany you. So Abu Sa’id got up with him and testified.  

كُنْتُ جَالِسًا فِي مَجْلِسٍ مِنْ مَجَالِسِ الأَنْصَارِ فَجَاءَ أَبُو مُوسَى فَزِعًا فَقُلْنَا لَهُ مَا أَفْزَعَكَ قَالَ أَمَرَنِي عُمَرُ أَنْ آتِيَهُ فَأَتَيْتُهُ فَاسْتَأْذَنْتُ ثَلاَثًا فَلَمْ يُؤْذَنْ لِي فَرَجَعْتُ فَقَالَ مَا مَنَعَكَ أَنْ تَأْتِيَنِي قُلْتُ قَدْ جِئْتُ فَاسْتَأْذَنْتُ ثَلاَثًا فَلَمْ يُؤْذَنْ لِي وَقَدْ قَالَ رَسُولُ اللَّهِ ﷺ إِذَا اسْتَأْذَنَ أَحَدُكُمْ ثَلاَثًا فَلَمْ يُؤْذَنْ لَهُ فَلْيَرْجِعْ قَالَ لَتَأْتِيَنِّي عَلَى هَذَا بِالْبَيِّنَةِ قَالَ فَقَالَ أَبُو سَعِيدٍ لاَ يَقُومُ مَعَكَ إِلاَّ أَصْغَرُ الْقَوْمِ قَالَ فَقَامَ أَبُو سَعِيدٍ مَعَهُ فَشَهِدَ لَهُ  

We were in the company of Ubayy b. Ka'b that Abu Musa Ash'ari came there in a state of anger. He stood (before us) and said: I ask you to bear witness in the name of Allah whether anyone amongst you heard Messenger of Allah ﷺ as saying: Permission (for entering the house) should be sought three times and if permission is granted to you (then get in). otherwise go back. Ubayy b. Ka'b said: What is the iiiatter? He said: I sought permission yesterday from 'Umar b. Khattab three times but he did not permit me, so I came back; then I went to him today and visited him and informed him that I had come to him yesterday and greeted him thrice, then came back, whereupon he said: Yes, we did hear you but be were at that time busy, but why did you not seek permission (further and you must have never gone back until you were permitted to do so). He said: I sought permission (in the manner) that I heard Messenger of Allah ﷺ having said (in connection 'With the seeking of permission for entering the house of a stranger). Thereupon he (Hadrat Umar) said: By Allah, I shall torture your back and your stomach unless you bring one who may bear witness to what you state. 'Ubayy b. Ka'b said: By Allah, none should stand with you (to bear testimony) but the youngest amongst us. And he therefore, said to Abu Sa'id: Stand up. So I stood up until I came to Umar and said: I heard Messenger of Allah ﷺ say this. (Using translation from Muslim 2153c)  

سَمِعَ أَحَدٌ مِنْكُمْ رَسُولَ اللَّهِ ﷺ يَقُولُ «الِاسْتِئْذَانُ ثَلَاثٌ فَإِنْ أُذِنَ لَكَ وَإِلَّا فَارْجِعْ»؟ قَالَ أُبَيٌّ وَمَا ذَاكَ؟ قَالَ اسْتَأْذَنْتُ عَلَى عُمَرَ بْنِ الْخَطَّابِ أَمْسِ ثَلَاثَ مَرَّاتٍ فَلَمْ يُؤْذَنْ لِي فَرَجَعْتُ ثُمَّ جِئْتُهُ فَدَخَلْتُ عَلَيْهِ فَأَخْبَرْتُهُ أَنِّي جِئْتُهُ أَمْسِ فَسَلَّمْتُ ثَلَاثًا ثُمَّ انْصَرَفْتُ فَقَالَ قَدْ سَمِعْنَاكَ وَنَحْنُ حِينَئِذٍ عَلَى شُغْلٍ فَلَوِ اسْتَأْذَنْتَ حَتَّى يُؤْذَنَ لَكَ؟ قَالَ اسْتَأْذَنْتُ كَمَا سَمِعْتُ رَسُولَ اللَّهِ ﷺ قَالَ فَوَاللَّهِ لَأُوجِعَنَّ ظَهْرَكَ أَوْ لَتَأْتِيَنِّي بِمَنْ يَشْهَدُ لَكَ عَلَى هَذَا قَالَ فَقَالَ أُبَيٌّ وَاللَّهِ لَا يَقُومُ مَعَكَ إِلَّا أَحْدَثُنَا سِنًّا قُمْ يَا أَبَا سَعِيدٍ فَقُمْتُ حَتَّى أَتَيْتُ عُمَرَ فَقُلْتُ قَدْ سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ هَذَا