Musannaf Ibn Abi Shayba 33:628

Waki’ narrated to us, from al-A’mash, from Mundhir, from al-Rabi’ that he said to his family, "Make *khabis* (a sweet dish) for me." So they made it. Then he invited a man who was afflicted with madness, and al-Rabi’ began feeding him by hand while his saliva was flowing. When he had eaten and left, his family said to him, "We went to the trouble of making it, and then you fed it to someone who does not even know what he ate." Al-Rabi’ said, "But Allah knows."