بُلُوغُ الْمَرَامِ
Bulugh al-Maram 223
The Book of Prayer
وَعَنْ مُطَرِّفِ بْنِ عَبْدِ اَللَّهِ بْنِ الشِّخِّيرِ , عَنْ أَبِيهِ قَالَ : { رَأَيْتُ رَسُولَ اَللَّهِ - صلى الله عليه وسلم -يُصَلِّي , وَفِي صَدْرِهِ أَزِيزٌ كَأَزِيزِ اَلْمِرْجَلِ , مِنْ اَلْبُكَاءِ } أَخْرَجَهُ اَلْخَمْسَةُ , إِلَّا اِبْنَ مَاجَهْ , وَصَحَّحَهُ اِبْنُ حِبَّانَ . [1]
Narrated Mutarrif bin Abdullah bin Shikhkhir (RA) from his father, who said, "I saw Allah's Messenger (ﷺ) when he was engaged in prayer, and heard a sound from his chest, like the bubbling of a pot, from weeping." [Reported by al-Khamsah except Ibn Majah, and Ibn Hibban graded it Sahih (authentic)].
Sunnah.com reference: Book 2, Hadith 88