It is narrated from Sayyiduna Abu Ayyub (may Allah be pleased with him) that he (peace and blessings be upon him) sent him some food with a green dish containing onion or leek. He did not see in it the marks of the fingers of the Messenger of Allah (peace and blessings be upon him), so he refused to eat it. The Messenger of Allah (peace and blessings be upon him) said to him: "What stopped you from eating?" He said: O Messenger of Allah! I did not see your mark in it. The Messenger of Allah (peace and blessings be upon him) said: "I feel shy before the angels of Allah; otherwise it is not forbidden."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 3981