Abdullah bin Dinar (may Allah have mercy on him) said: Two men came to Sayyiduna Abdullah bin Umar (may Allah be pleased with them both). Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) asked: "Where have you come from?" They said: "From Sayyiduna Abdullah bin al-Zubayr (may Allah be pleased with them both), and he has made lawful for us things that used to be forbidden to us." Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) asked: "What has he made lawful for you of what was forbidden to you?" They said: "He has permitted us the sale of ummahat al-awlad." He said: "Do you know Abu Hafs, Sayyiduna Umar (may Allah be pleased with him)?" They said: "Yes." He said: "He forbade the sale of ummahat al-awlad, giving them as gifts or making them part of an inheritance. Her master may enjoy her during his lifetime, and when he dies she is free."
This is how the group narrated it from Abdullah bin Dinar. Some narrators erred in it from Abdullah bin Dinar and raised it to the Prophet (peace and blessings be upon him); that is an error which it is not permissible to mention.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21765