Musannaf Ibn Abi Shayba 13:2217

Abu Bakr narrated to us, he said: Yahya ibn Abi Bukayr narrated to us, from Zuhayr ibn Muhammad, from Abdullah ibn Muhammad ibn Aqil, from Abdullah ibn Sahl ibn Hunayf, that Sahl narrated to him that the Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever helps a fighter in the way of Allah, or a debtor in his hardship, or a slave (mukātab) in his neck (i.e., his manumission), Allah will shade him in His shade on the day when there is no shade except His shade."