Musnad Ahmad 435:8

'Ali ibn Bahr narrated to us, he said: Marhum ibn 'Abd al-'Aziz narrated to me, he said: Abu Na'amah al-Sa'di narrated to me, from Abu 'Uthman al-Nahdi, from Abu Sa'id al-Khudri, who said: Mu'awiyah went out to a circle in the mosque and said: "What has made you sit?" They said: "We sat to remember Allah, the Almighty and Majestic." He said: "By Allah, nothing has made you sit except that?" They said: "By Allah, nothing has made us sit except that." He said: "As for me, I did not ask you to swear out of suspicion of you, and there was no one in my position relative to the Messenger of Allah, may Allah bless him and grant him peace, who narrated fewer hadiths from him than I. The Messenger of Allah, may Allah bless him and grant him peace, went out to a circle of his companions and said: 'What has made you sit?' They said: 'We sat to remember Allah, the Almighty and Majestic, and to praise Him for guiding us to Islam and bestowing favor upon us through you.' He said: 'By Allah, nothing has made you sit except that?' They said: 'By Allah, nothing has made us sit except that.' He said: 'As for me, I did not ask you to swear out of suspicion of you. Indeed, Gabriel, peace be upon him, came to me and informed me that Allah, the Almighty and Majestic, is boasting of you to the angels.'"