'Abdullah bin Shikh-kheer Radiyallahu 'Anhu says:
"I attended the noble assembly of Rasulullah Sallallahu 'Alayhi Wasallam. He was performing salaah. Because of his crying, such sound emmitted from his chest, like that of a boiling pot". (ES)
English reference (ES): Book 44, Hadith 305 (ES)
Arabic reference (ES): Book 45, Hadith 322 (ES)