Sahih Muslim , Book 38, Hadith 44 (In-Book) ⓘ

Abu Sa'id reported that Abu Musa al-Ash'ari came to the door of 'Umar and sought his permission (to get into his house). Umar said: That is once. He again sought permission for the second time and 'Umar said: It is twice. He again sought permission for the third time and Umar said: It is thrice. He (Abu Musa) then went back. He (Hadrat 'Umar) (sent someone) to pursue him so that he should be brought back. Thereupon he (Hadrat Umar) said: If this act (of yours is in accordance with the command of Allah's Messenger you have preserved in your mind, then it is all right, otherwise (I shall give you such a severe punishment) that it will serve as an example to others. Abu Sa'id said: Then he (Abu Musa) came to us and said: Do you remember Allah's Messenger having said this:" Permission is for three times"? They (Companions sitting in that cothpany) began to laugh, whereupon he (Abu Musa) said: There comes to you your Muslim brother who had been perturbed and you laugh. Abu Sa'id said: (Well), you go forth. I shall be your participant in this trouble of yours. So he came to him (Hadrat Umar) and said: Here is Abu Sa'id (to support my statement).

حَدَّثَنَا نَصْرُ بْنُ عَلِيٍّ الْجَهْضَمِيُّ، حَدَّثَنَا بِشْرٌ، - يَعْنِي ابْنَ مُفَضَّلٍ - حَدَّثَنَا سَعِيدُ، بْنُ يَزِيدَ عَنْ أَبِي نَضْرَةَ، عَنْ أَبِي سَعِيدٍ، أَنَّ أَبَا مُوسَى، أَتَى بَابَ عُمَرَ فَاسْتَأْذَنَ فَقَالَ عُمَرُ وَاحِدَةٌ ‏.‏ ثُمَّ اسْتَأْذَنَ الثَّانِيَةَ فَقَالَ عُمَرُ ثِنْتَانِ ‏.‏ ثُمَّ اسْتَأْذَنَ الثَّالِثَةَ فَقَالَ عُمَرُ ثَلاَثٌ ‏.‏ ثُمَّ انْصَرَفَ فَأَتْبَعَهُ فَرَدَّهُ فَقَالَ إِنْ كَانَ هَذَا شَيْئًا حَفِظْتَهُ مِنْ رَسُولِ اللَّهِ صلى الله عليه وسلم فَهَا وَإِلاَّ فَلأَجْعَلَنَّكَ عِظَةً ‏.‏ قَالَ أَبُو سَعِيدٍ فَأَتَانَا فَقَالَ أَلَمْ تَعْلَمُوا أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ الاِسْتِئْذَانُ ثَلاَثٌ ‏" ‏ ‏.‏ قَالَ فَجَعَلُوا يَضْحَكُونَ - قَالَ - فَقُلْتُ أَتَاكُمْ أَخُوكُمُ الْمُسْلِمُ قَدْ أُفْزِعَ تَضْحَكُونَ انْطَلِقْ فَأَنَا شَرِيكُكَ فِي هَذِهِ الْعُقُوبَةِ ‏.‏ فَأَتَاهُ فَقَالَ هَذَا أَبُو سَعِيدٍ ‏.‏