Amir (may Allah have mercy on him) said concerning this verse, "And if one of you entrusts another" [Surah al-Baqarah: 283]: "If you take witnesses, that is prudence; and if you trust him, that is permissible and there is latitude in it."
(b) Al-Hasan al-Basri (may Allah have mercy on him) said: "If he wishes he may take witnesses, and if he wishes he may not take witnesses. Have you not heard the words of Allah: 'And if one of you entrusts another' [Surah al-Baqarah: 283]?" Imam al-Shafi'i (may Allah have mercy on him) said: It is preserved that the Prophet (peace and blessings be upon him) concluded a sale of a horse with a Bedouin, and the Bedouin denied it at the prompting of some of the hypocrites, and there was no evidence between them.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب آداب القاضي / 20514