Sunan Ibn Majah 112
It was narrated that 'Aishah said:
The Messenger of Allah said: "O 'Uthman, if Allah places you in authority over this matter (as the caliph) some day and the hypocrites want to rid you of the garment with which Allah has clothed you (i.e., the position of caliph), do not take it off." He said that three times. (One of the narrators) Nu'man said: "I said to 'Aishah: 'What kept you from telling the people that?' She said: 'I was made to forget it.'"
حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا أَبُو مُعَاوِيَةَ، حَدَّثَنَا الْفَرَجُ بْنُ فَضَالَةَ، عَنْ رَبِيعَةَ بْنِ يَزِيدَ الدِّمَشْقِيِّ، عَنِ النُّعْمَانِ بْنِ بَشِيرٍ، عَنْ عَائِشَةَ، قَالَتْ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏
"‏ يَا عُثْمَانُ إِنْ وَلاَّكَ اللَّهُ هَذَا الأَمْرَ يَوْمًا فَأَرَادَكَ الْمُنَافِقُونَ أَنْ تَخْلَعَ قَمِيصَكَ الَّذِي قَمَّصَكَ اللَّهُ فَلاَ تَخْلَعْهُ ‏"‏ ‏.‏ يَقُولُ ذَلِكَ ثَلاَثَ مَرَّاتٍ ‏.‏ قَالَ النُّعْمَانُ فَقُلْتُ لِعَائِشَةَ مَا مَنَعَكِ أَنْ تُعْلِمِي النَّاسَ بِهَذَا قَالَتْ أُنْسِيتُهُ وَاللَّهِ ‏.‏