From Sahih Bukhari (Hadith 4000):
Narrated `Aisha:(the wife of the Prophet) Abu Hudhaifa, one of those who fought the battle of Badr, with Allah's Apostle adopted Salim as his son and married his niece Hind bint Al-Walid bin `Utba to him and Salim was a freed slave of an Ansari woman. Allah's Messenger (ﷺ) also adopted Zaid as his son. In the pre-Islamic period of ignorance the custom was that, if one adopted a son, the people would call him by the name of the adopted-father whom he would inherit as well, till Allah revealed: "Call them (adopted sons) By (the names of) their fathers
Reference: Bukhari 4000