Ubaydah narrates from Sayyiduna Ali (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said about the captives of Badr: "If you wish, kill them, or if you wish, take ransom and benefit from the ransom, and (then) the same number of your companions will be martyred." He says: Thabit bin Qays (may Allah be pleased with him) was the last of those seventy; he was martyred on the day of Yamamah.
(b) Al-Burullusi added in his narration that Ibn Ar'arah said: I put this matter back to Azhar, but he refused (to change it) and insisted on saying: Ubaydah narrates from Ali (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18040