Musnad Ahmad 28:9

'Abd al-A'la narrated to us, from Ma'mar, from al-Zuhri, from Sa'id ibn al-Musayyib, from 'Abdullah ibn 'Amr ibn al-'As, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, the just (al-muqsitun) in this world will be upon pulpits of pearl on the Day of Resurrection, in front of the Most Merciful, because they were just in the world."