Al-Kāfi - Volume 5 > Loan That Brings Profit
Hadith #4

4- أَبُو عَلِيٍّ الأشْعَرِيُّ عَنْ مُحَمَّدِ بْنِ عَبْدِ الْجَبَّارِ عَنْ صَفْوَانَ عَنْ عَبْدِ الرَّحْمَنِ بْنِ الْحَجَّاجِ قَالَ سَأَلْتُ أَبَا الْحَسَنِ (عَلَيْهِ السَّلام) عَنِ الرَّجُلِ يَجِيئُنِي فَأَشْتَرِي لَهُ الْمَتَاعَ مِنَ النَّاسِ وَأَضْمَنُ عَنْهُ ثُمَّ يَجِيئُنِي بِالدَّرَاهِمِ فَ‏آخُذُهَا وَأَحْبِسُهَا عَنْ صَاحِبِهَا وَآخُذُ الدَّرَاهِمَ الْجِيَادَ وَأُعْطِي دُونَهَا فَقَالَ إِذَا كَانَ يَضْمَنُ فَرُبَّمَا اشْتَدَّ عَلَيْهِ فَعَجَّلَ قَبْلَ أَنْ يَأْخُذَهُ وَيَحْبِسُ بَعْدَ مَا يَأْخُذُ فَلا بَأْسَ.

4. Abu Ali al-Ash’ariy has narrated from Muhammad ibn ‘Abd al-Jabbar from Safwan from ‘Abd al-Rahman ibn al-Hajjaj who has said the following: “I once asked abu al-Hassan, ‘Alayhi al-Salam, about the case of a man who came to me; I bought for him goods from people and guaranteed payment on his behalf. Then he came to me with dirham. I took and withheld them from their owner, then took the good quality dirhams and gave them of lower quality. He (the Imam) said, ‘He guaranteed payment, perhaps it became severe upon him so he hurried to pay before he (the guarantor) asks for payment. He (the guarantor) withholds payment after receiving, it is not unlawful.’”