It is narrated from Abdullah bin Dinar that a man came to Abdullah bin Umar (may Allah be pleased with them both) while I was with him near the court, and he asked Abdullah bin Umar (may Allah be pleased with them both) about the nursing of an adult. Ibn Umar (may Allah be pleased with them both) said: A man came to Umar bin al-Khattab (may Allah be pleased with him) and said: I have a slave woman and I used to have intercourse with her. My wife went to her and nursed her with her own milk. When I went in to her, my wife said: Keep away, by Allah, I have nursed her. Umar (may Allah be pleased with him) said: Punish her (your wife), and go to your slave woman, that is, have intercourse with her. Fosterage is only established at a young age.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرضاع / 15659