مُسْنَدُ أَحْمَدَ
Musnad Ahmad 1910
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated from Ibn "Abbas that he said: When he prayed Fair he would lie down until he began to breathe deeply, and we used to say to ‘Amr: The Messenger of Allah (ﷺ) said: “My eyes sleep but my heart does not."
Musnad Ahmad 1911Sahih (Darussalam) [ al-Bukhari (138) and Muslim (763)]