Hadith Qudsi 14:

Narrated Abu Hurairah: the Prophet said:

Allah Almighty has supernumerary angels who rove about seeking out gatherings in which Allah's name is being invoked: they sit with them and fold their wings round each other, filling in that which is between them and between the lowest heaven. When [the people in the gathering] depart, [the angels] ascend and rise up to heaven." He (the Prophet - peace and blessings of Allah be upon him) said: "Then Allah (mighty and sublime be He) asks them - [though] He is most knowing about them: ‘From where have you come?’ And they say: ‘We have come from some servants of Yours on Earth: they were glorifying You (Subhana llah), exalting you (Allahu akbar), witnessing that there is no god but You (La ilaha illa llah), praising You (Al-Hamdu lillah), and asking [favours] of You.’ He says: ‘And what do they ask of Me?’ They say: ‘They ask of You Your Paradise.’ He says: ‘And have they seen My Paradise?’ They say: ‘No, O Lord.’ He says: ‘And how would it be were they to have seen My Paradise!’ They say: ‘And they ask protection of You.’ He says: ‘From what do they ask protection of Me?’ They say: ‘From Your Hell-fire, O Lord.’ He says: ‘And have they seen My Hell-fire?’ They say: ‘No.’ He says: ‘And how would it be were they to have seen My Hell-fire!’ They say: ‘And they ask for Your forgiveness.’" He (the Prophet - peace and blessings of Allah be upon him) said: "Then He says: ‘I have forgiven them and I have bestowed upon them what they have asked for, and I have granted them sanctuary from that from which they asked protection.’" He (the Prophet - peace and blessings of Allah be upon him) said: "They say: ‘O Lord, among then is So-and-so, a much sinning servant, who was merely passing by and sat down with them.’" He (the Prophet - peace and blessings of Allah be upon him) said: "And He says: ‘And to him [too] I have given forgiveness: he who sits with such people shall not suffer.’

It was related by Muslim (also by al-Bukhari, at-Tirmidhi, and an-Nasa'i).