Musnad Ahmad 33:390

Muhammad ibn Bishr narrated to us, Muhammad ibn ‘Amr narrated to us, Yazid ibn ‘Abdullah ibn Usamah al-Laythi and Yahya ibn Sa‘id narrated to me, from Mu‘adh ibn Rifa‘ah al-Zuraqi, from Jabir ibn ‘Abdullah, who said: The Messenger of Allah (ﷺ) said: "For this righteous servant, for whom the Throne shook, and the gates of the heaven were opened, it was made difficult for him, then Allah relieved him." And he said once: "Were opened." And he said once: "Then Allah relieved him." And he said once: The Messenger of Allah (ﷺ) said regarding Sa‘d on the day he died, while he was being buried.