Musnad Ahmad 27:1563

Ya'qub ibn Ibrahim narrated to us, 'Asim ibn Muhammad narrated to us, from his brother 'Umar ibn Muhammad, from Muhammad ibn Zayd, from Ibn 'Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "When the people of Paradise have arrived in Paradise"—and he mentioned the rest of it.