Musnad Ahmad 535:9

Hassan narrated to us, Ibn Lahi'ah narrated to us, Haywah bin Shurayh narrated to us, from 'Uqbah bin Muslim, who said: I heard 'Abdullah bin al-Harith bin Juz' al-Zubaydi say: I heard the Messenger of Allah (ﷺ) say: "Woe to the heels and the soles of the feet from the Fire." Harun narrated to us, 'Abdullah bin Wahb narrated to us, 'Amr narrated to us, that Sulayman bin Ziyad al-Hadrami narrated to him, that 'Abdullah bin al-Harith bin Juz' al-Zubaydi narrated to him: That he and a companion of his passed by Ayman and some youths of Quraysh who had loosened their waist-wrappers and made them into whips, striking one another with them while they were naked. 'Abdullah said: When we passed by them, they said: "These are monks, so leave them alone." Then the Messenger of Allah (ﷺ) came out to them. When they saw him, they scattered. The Messenger of Allah (ﷺ) returned in anger until he entered, and I was behind the chamber, and I heard him saying: "Subhan Allah! They were neither ashamed before Allah, nor did they cover themselves before His Messenger." Umm Ayman was with him, saying: "Ask forgiveness for them, O Messenger of Allah." 'Abdullah said: "So with difficulty, he asked forgiveness for them." 'Abdullah said: And I heard it myself from Harun.