Business Transactions which are Forbidden - Section 2 Mishkat al-Masabih 2861
Arabic hadith text
عَنْ جَابِرٍ قَالَ: إِنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ نَهَى عَنِ الثُّنْيَا إِلَّا أنْ يُعلمَ. رَوَاهُ التِّرْمِذِيّ
Translation
Jabir said that God’s Messenger forbade making an exception unless it was explicit. Tirmidhi transmitted it.