The Quran

وَإِذ أَسَرَّ النَّبِيُّ إِلىٰ بَعضِ أَزواجِهِ حَديثًا فَلَمّا نَبَّأَت بِهِ وَأَظهَرَهُ اللَّهُ عَلَيهِ عَرَّفَ بَعضَهُ وَأَعرَضَ عَن بَعضٍ ۖ فَلَمّا نَبَّأَها بِهِ قالَت مَن أَنبَأَكَ هٰذا ۖ قالَ نَبَّأَنِيَ العَليمُ الخَبيرُ

Muhammad Asad

And lo!¹ [It so happened that] the Prophet told something in confidence to one of his wives; and when she thereupon divulged it, and God made this known to him, he acquainted [others] with some of it and passed over some of it.² And as soon as he let her know it, she asked, "Who has told thee this?"³ - [to which] he replied, "The All-Knowing, the All-Aware has told me."

See surah 2, note 21.
Lit., "he turned aside from [or "avoided"] some of it". There is no reliable Tradition as to the subject of that confidential information. Some of the early commentators, however, connect it with the Prophet's veiled prediction that Abu Bakr and Umar ibn al-Khattab would succeed him as leaders of the Muslim community; the recipient of the information is said to have been Hafsah, the daughter of Umar, and the one to whom she disclosed it, A'ishah, the daughter of Abu Bakr (Baghawi, on the, authority of Ibn Abbas and Al-Kalbi; also Zamakhshari). If this interpretation is correct, it would explain why the Prophet "acquainted [others] with some of it and passed over some of it": for, once his confidential prediction had been divulged, he saw no point in withholding it any longer from the community; nevertheless, he alluded to it in deliberately vague terms - possibly in order not to give to the succession of Abu Bakr and Umar the appearance of all "apostolic sanction" but to leave it, rather to a free decision of the community in pursuance of the Qur'anic principle amruhum shura baynahum (see 42:38).
I.e., that she had broken the Prophet's confidence.