Musnad Ahmad 33:756

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, Mu'adh ibn Rifa'ah al-Ansari, then al-Zuraqi, narrated to me, from Mahmud ibn 'Abd al-Rahman ibn 'Amr ibn al-Jamuh, from Jabir ibn 'Abd Allah al-Ansari, who said: We went out one day with the Messenger of Allah, may Allah bless him and grant him peace, to Sa'd ibn Mu'adh when he died. He said: When the Messenger of Allah, may Allah bless him and grant him peace, had prayed over him and he was placed in his grave and leveled, the Messenger of Allah, may Allah bless him and grant him peace, glorified Allah (said *SubhanAllah*), and we glorified Allah for a long time. Then he magnified Allah (said *Allahu Akbar*), and we magnified Allah. It was said: "O Messenger of Allah, why did you glorify Allah, then magnify Him?" He said: "This righteous servant’s grave became constricted upon him, until Allah relieved it for him."