Sayyiduna Abu Mas'ud (may Allah be pleased with him) said: There was a man among us called Abu Shu'ayb, and he had a slave who was a butcher. He said to his slave: "Prepare food for me; perhaps I may invite the Prophet (peace and blessings be upon him)." So he invited the Prophet (peace and blessings be upon him) as the fifth of five, and another man followed them. The Prophet (peace and blessings be upon him) said to the man: "You invited me as the fifth of five, and this man has followed us. If you permit (him, well and good); otherwise he will go back." He said: "No, rather we permit him."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14596