Sunan At-Tirmidhi

Ubaidullah bin Abdullah bin Mas'ud narrated from his father (Abdullah bin Mas'ud) that he said:""When Allah's Messenger sat for the first two Rak'ah it was as if he was on hot stones."" Shu'bah (one of the narrators) said: ""Then Sa'd's lips moved (saying) something. So I said: 'Until he stood?' He said: 'Until he stood