Musannaf Ibn Abi Shayba 6:1245

Sulayman ibn Harb narrated to us, Hammad ibn Salamah narrated to us, from ‘Asim ibn Bahdalah, from Habib ibn Abi Jubayrah, from Ya‘la ibn Shababah: That the Prophet, may Allah bless him and grant him peace, passed by a grave whose occupant was being punished. He said, "Indeed, the occupant of this grave is being punished for something that is not major." Then he called for a palm branch and placed it upon his grave, then said, "Perhaps it will be lightened for him as long as it remains moist."