Ja'far bin Muhammad narrates from his father, from his grandfather, that Sayyiduna Abu Usayd al-Ansari (may Allah be pleased with him) brought captives from Bahrain, and they were lined up in rows. The Prophet (peace and blessings be upon him) stood and looked at them, and a woman was weeping. He (peace and blessings be upon him) asked: "What has made you weep?" She said: My son has been sold among the tribe of Abs. So the Prophet (peace and blessings be upon him) said to Sayyiduna Abu Usayd (may Allah be pleased with him): "You must ride and bring him back, for the price at which you sold him." So Sayyiduna Abu Usayd (may Allah be pleased with him) rode and brought him back.
This, although it has irsal (a missing link) in it, is a good mursal report, a corroboration of what preceded.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18308