Musnad Ahmad 31:747

'Affan narrated to us, Hammad ibn Salamah narrated to us, 'Ata' ibn al-Sa'ib informed us, from 'Ubayd Allah ibn 'Abd Allah ibn 'Utbah, from Abu Sa'id al-Khudri, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Paradise and the Fire boasted to one another. The Fire said: 'O Lord, the tyrants, the kings, the great ones, and the noble ones enter me.' And Paradise said: 'O Lord, the poor, the weak, and the destitute enter me.' So the Blessed and Exalted said to the Fire: 'You are My punishment; I afflict with you whom I will.' And He said to Paradise: 'You are My mercy; you encompass everything. And for each of you is its filling.' As for the Fire, its people will be cast into it, and it will say: 'Are there any more?' until the Blessed and Exalted comes to it and places His foot upon it, so it will shrink and say: 'Enough, enough.' As for Paradise, it will remain as long as Allah wills it to remain, then Allah will create for it a creation as He wills." Hasan al-Ashyab said: "As for Paradise, it will remain as long as Allah wills it to remain."