Abdullah b. Ja'far reported that one day Messenger of Allah ﷺ mounted me behind him and narrated to me something in secret which I would narrate to none amongst people. (Using translation from Muslim 2429)   

أَرْدَفَنِي رَسُولُ اللَّهِ ﷺ ذَاتَ يَوْمٍ خَلْفَهُ فَأَسَرَّ إِلَيَّ حَدِيثًا لَا أُحَدِّثُ بِهِ أَحَدًا مِنَ النَّاسِ وَكَانَ «أَحَبَّ مَا اسْتَتَرَ النَّبِيُّ ﷺ لِحَاجَتِهِ هَدَفٌ أَوْ حَائِشُ نَخْلٍ»