It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever frees a slave, the slave's property belongs to him (the slave), unless the master stipulates his property for himself, in which case that property belongs to the master."
Hadith Referenceالمعجم الأوسط / باب الميم / 8730
Hadith Takhrij«أخرجه النسائي فى «السنن الكبرى» برقم: 4961، 4962، وأبو داود فى «سننه» برقم: 3962، وابن ماجه فى «سننه» برقم: 2529، والبيهقي فى «السنن الكبرى» برقم: 10874، والدارقطني فى «سننه» برقم: 4244، 4245»