Musnad Ahmad 1060:88

'Abd al-Malik ibn 'Amr narrated to us, Kathir ibn Zayd narrated to us, from Dawud ibn Abi Salih, who said: Marwan approached one day and found a man placing his face upon the grave. He said, "Do you know what you are doing?" The man turned toward him, and it was Abu Ayyub. He said, "Yes. I came to the Messenger of Allah (peace and blessings of Allah be upon him), and I did not come to a stone. I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: 'Do not weep for the religion when its people are in charge of it, but weep for it when those who are not its people are in charge of it.'"