Sunan an-Nasa'i 3935
It was narrated that Muhammad said:
"I do not know that Shuraih ever ruled on Mudarabah disputes except in two ways. He would say to the Mudarib (the one who contributed his labor to the partnership): 'You must provide proof that a calamity befell you so that you may be excused.' Or he would say to the one who invested his money in the partnership: 'You must provide proof that your trustee betrayed his trust, otherwise his oath sworn by Allah that he did not betray you is sufficient.'"
أَخْبَرَنَا عَمْرُو بْنُ زُرَارَةَ، قَالَ حَدَّثَنَا إِسْمَاعِيلُ، عَنْ أَيُّوبَ، عَنْ مُحَمَّدٍ، قَالَ لَمْ أَعْلَمْ شُرَيْحًا كَانَ يَقْضِي فِي الْمُضَارِبِ إِلاَّ بِقَضَاءَيْنِ كَانَ رُبَّمَا قَالَ لِلْمُضَارِبِ بَيِّنَتَكَ عَلَى مُصِيبَةٍ تُعْذَرُ بِهَا‏.‏‏ وَرُبَّمَا قَالَ لِصَاحِبِ الْمَالِ بَيِّنَتَكَ أَنَّ أَمِينَكَ خَائِنٌ وَإِلاَّ فَيَمِينُهُ بِاللَّهِ مَا خَانَكَ‏.‏‏