Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says that a man from Banu Sahm set out with Tamim al-Dari and Adi bin Badda'. The Sahmi died in a land where there was no Muslim. When the two of them brought his estate, (his heirs) found missing a silver goblet inlaid with gold. The Prophet (peace and blessings be upon him) made the two of them swear oaths. Then the goblet was found in Makkah, and (those who had it) said: We bought it from Tamim and Adi. Then two of the heirs of the Sahmi stood up and swore that our testimony is more rightful than their testimony, and that the goblet belongs to their companion. Concerning them this verse was revealed: 'O you who believe! The testimony among you' [Surah al-Ma'idah: 106].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الشهادات / 20625