"I came to the Prophet ﷺ when he was praying, and there was a sound coming from his chest like the sound of water boiling," meaning, he was weeping.  

أَتَيْتُ النَّبِيَّ ﷺ وَهُوَ يُصَلِّي وَلِجَوْفِهِ أَزِيزٌ كَأَزِيزِ الْمِرْجَلِ يَعْنِي يَبْكِي