that when the verse: O you wrapped up in your mantle, stand vigil through the night, except a little descended onto the Prophet (SAWA), he used to stay up all night until his feet would swell up, so he would pick one foot up, and put the other down, and Gabriel came down to him saying: Taha, meaning 'the earthis for your feet, O Muhammad', We did not send down to you the Qur'an that you should be miserable , and He revealed: So recite as much of the Qur'an as is feasible.'
Imam Ali ibn Abi Talib [as]
Tafsir al-Mizan, v. 14, no. 126