It is narrated from Sayyiduna Amr bin Awf bin Milhah al-Muzani (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "In Islam, a helpless person (without a tribe) is not to be left just like that." Ibn Numayr added in his narration: "until he is attached to a tribe."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14108