Mishkat al-Masabih 11 Business Transactions كتاب البيوع 170

وَعَنْهُ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «أَدِّ الْأَمَانَةَ إِلَى مَنِ ائْتَمَنَكَ وَلَا تَخُنْ مَنْ خَانَكَ» . رَوَاهُ التِّرْمِذِيُّ وَأَبُو دَاوُدَ وَالدَّارِمِيُّ

He reported the Prophet as saying, “Place trust in him who trusts you, but do not cheat him who cheats you.” Tirmidhi, Abu Dawud and Darimi transmitted it.