أَخْبَرَنَا سُوَيْدُ بْنُ نَصْرٍ، قَالَ أَنْبَأَنَا عَبْدُ اللَّهِ، عَنْ حَمَّادِ بْنِ سَلَمَةَ، عَنْ ثَابِتٍ الْبُنَانِيِّ، عَنْ مُطَرِّفٍ، عَنْ أَبِيهِ، قَالَ أَتَيْتُ النَّبِيَّ صلى الله عليه وسلم وَهُوَ يُصَلِّي وَلِجَوْفِهِ أَزِيزٌ كَأَزِيزِ الْمِرْجَلِ يَعْنِي يَبْكِي ‏.‏

It was narrated from Mutarrif that his father said: "I came to the Prophet (PBUH) when he was praying, and there was a sound coming from his chest like the sound of water boiling," meaning, he was weeping. Translation Not Available

Book reference: Sunan An Nisai Book 13 Hadith 1214
Web reference: Sunan An Nisai Volume 2 Book 13 Hadith 1215