Mishkat al-Masabih #941

Mutarrif b. ‘Abdallah ash-Shikhkhir quoted his father as saying, “I came to the Prophet when he was engaged in prayer, and heard a sound from within him like the bubbling of a pot,” meaning that he was weeping. In a version he said, “I saw the Prophet praying and a sound came from his breast like the rumbling of a mill, owing to weeping.” Ahmad transmitted it. Nasa’i transmitted the first version and Abu Dawud the second.