It is narrated from Sayyiduna Abu Jamilah (may Allah be pleased with him) that he found a foundling in the time of the Messenger of Allah (peace and blessings be upon him) and brought him (to Umar). Sayyiduna Umar (may Allah be pleased with him) suspected him, then he was praised well, so Sayyiduna Umar (may Allah be pleased with him) said: "He is free, his wala' (patronage) is yours, and his maintenance will be from the public treasury (Bayt al-Mal)."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6469