This hadith has been transmitted on the authority of Mughira b. Shu'ba and the words are:Allah's Apostle (ﷺ) kept standing in prayer (for such long hours) that his feet were swollen. They (his Companions) said: Verily, Allah has pardoned for thee the earlier and the later of thine sins. Thereupon he said: Should I not prove myself to be a grateful servant (of Allah)?
A'isha reported that when Allah's Messenger (ﷺ) occupied himself in prayer, he observed such a (long) qiyam (posture of standing in prayer) that his feet were swollen. A'isha said:Allah's Messenger you do this (in spite of the fact) that your earlier and later sins have been pardoned for you? Thereupon, he said. A'isha should I not prove myself to be a thanksgiving servant (of Allah)?
Shaqiq reported:We were sitting at the door of Abdullah (b. Mas'ud) waiting for him (to come out and deliver a sermon to us). It was at this time that there happened to pass by us Yazid b. Mu'awiya an-Nakha'i. We said: Inform him ('Abdullah b. Mas'ud) of our presence here. He went in and Abdullah b. Mas'ud lost no time in coming out to us and said: I was informed of your presence here but nothing hindered me to come out to you but the fact that I did not like to bore you (by stuffing your minds with sermons) as Allah's Messenger (ﷺ) did not deliver us sermon on certain days fearing that it might prove to be boring for us
Shaqiq b. Wi'il reported that 'Abdullah used to give us sermon on every Thursday. A person said:Abu 'Abd al-Rahman, we love your talk and so we yearn (to listen to you) and earnestly desire that you should deliver us lecture every day. Thereupon he said: There is nothing to hinder me in giving you talk (every day) but the fact that you may be bored. Allah's Messenger (ﷺ) did not deliver sermons on certain days (fearing that we might be bored)