Musnad Ahmad 770:7

'Affan narrated to us, Hammad ibn Salamah narrated to us, from al-Hajjaj, from 'Amr ibn Murrah, from Zadhan, from Jarir ibn 'Abd Allah al-Bajali, that a man came and entered into Islam. The Messenger of Allah (ﷺ) was teaching him Islam while he was on his journey. The hoof of his camel entered into a jerboa's burrow, so his camel stumbled with him, and he died. The Messenger of Allah (ﷺ) came upon him and said: "He did a little and was rewarded much." Hammad said it three times. "The *lahd* (niche in the side of the grave) is for us, and the *shaqq* (trench in the center of the grave) is for others."