Sahih Bukhari

Narrated Aisha:Once the Prophet (ﷺ) came to me while a man was in my house. He said, ""O `Aisha! Who is this (man)?"" I replied, ""My foster brothers"" He said, ""O `Aisha! Be sure about your foster brothers, as fostership is only valid if it takes place in the suckling period (before two years of age)