Musnad Ahmad 962:155

Abu al-Mughirah narrated to us, Ma'an ibn Rifa'ah narrated to us, Ali ibn Yazid narrated to me, he said: I heard al-Qasim Abu 'Abd al-Rahman narrating from Abu Umamah, who said: The Prophet, peace and blessings of Allah be upon him, passed by on a day of intense heat towards Baqi' al-Gharqad. He said: The people were walking behind him. He said: When he heard the sound of sandals, that weighed upon his soul, so he sat down until he put them in front of him, so that nothing of pride might enter his soul. When he passed by Baqi' al-Gharqad, there were two graves in which two men had been buried. He said: The Prophet, peace and blessings of Allah be upon him, stopped and said: "Whom did you bury here today?" They said: O Prophet of Allah, such-and-such and such-and-such. He said: "They are being punished now and are being tested in their graves." They said: O Messenger of Allah, for what is that? He said: "As for one of them, he used not to protect himself from urine, and as for the other, he used to walk about with slander." He took a fresh palm branch and split it, then placed it upon the two graves. They said: O Prophet of Allah, why did you do that? He said: "So that it may be lightened for them." They said: O Prophet of Allah, and until when are they being punished? He said: "It is an unseen matter that no one knows except Allah." He said: "And were it not for the confusion of your hearts or your adding to the speech, you would have heard what I hear."