Sahih Al Bukhari (638)

عن عمرة بنت عبدالرحمن أن عائشة رضي الله عنها زوج النبي (صلى الله عليه وسلم) أخبرتها "أن رسول الله (صلى الله عليه وسلم) كان عندها وأنها سمعت صوت رجل يستأذن في بيت حفصة قالت عائشة فقلت يا رسول الله هذا رجل يستأذن في بيتك قالت فقال رسول الله (صلى الله عليه وسلم) أراه فلانا لعم حفصة من الرضاعة فقالت عائشة لو كان فلان حيا لعمها من الرضاعة دخل علي فقال رسول الله (صلى الله عليه وسلم) نعم إن الرضاعة تحرم ما يحرم من الولادة"

`Amra bint `Abdur-Rahman narrated that `A'ishah the wife of the Prophet (peace be upon him) told her uncle that once, while the Prophet (peace be upon him) was in her house, she heard a man asking Hafsa's permission to enter her house. `A'ishah said: "I said, 'O Allah's Messenger! I think the man is Hafsa's foster uncle.'" `A'ishah added: "O Allah's Messenger! There is a man asking the permission to enter your house." Allah's Messenger (peace be upon him) replied: "I think the man is Hafsa's foster uncle." `A'ishah said: "If so-and-so were living (i.e. her foster uncle) would he be allowed to visit me?" Allah's Messenger (peace be upon him) said: "Yes, he would, as the foster relations are treated like blood relations (in marital affairs)."