Sayyiduna Ghaylan bin Salamah (may Allah be pleased with him) said that Abu al-Sa'ib Rafi' (may Allah be pleased with him), who was Ghaylan's slave, fled to the Prophet (peace and blessings be upon him), and he (peace and blessings be upon him) freed him. Then Ghaylan (may Allah be pleased with him) also accepted Islam, and the Prophet (peace and blessings be upon him) returned his wala to Ghaylan (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الولاء / 21529
Yazid bin Abi Habib (may Allah have mercy on him) said that whenever the Messenger of Allah (peace and blessings be upon him) besieged a fortress and slaves came to him, he (peace and blessings be upon him) would free them; and when their master accepted Islam, he would return the wala to him.
This is munqati' (its chain is broken), and Ibn Lahi'ah is alone in narrating it, and Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الولاء / 21530