NASAI-KUBRA 549: from Muṭarrif from his father —
"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. (Using translation from Nasāʾī 1214)

الكبرى للنسائي ٥٤٩: عن مطرف عن أبيه —
أَتَيْتُ النَّبِيَّ ﷺ وَهُوَ يُصَلِّي وَلِجَوْفِهِ أَزِيزٌ كَأَزِيزِ الْمِرْجَلِ يَعْنِي يُبْكِي


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Nasāʾī's Kubrá > Ṣalāh (Prayer) > § [Machine] Crying in prayer
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