Chapter on Currency Exchange and Its Forms
Man Lā Yaḥḍuruh al-Faqīh|Volume 3|Book 2|Chapter 29
وَ سَأَلَ عَبْدُ اَللَّهِ بْنُ سِنَانٍ أَبَا عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ: عَنْ شِرَاءِ اَلْفِضَّةِ وَ فِيهَا اَلزِّيبَقُ وَ اَلرَّصَاصُ بِالْوَرِقِ وَ هِيَ إِذَا أُذِيبَتْ نَقَصَتْ مِنْ كُلِّ عَشَرَةٍ دِرْهَمَانِ أَوْ ثَلاَثَةٌ فَقَالَ "لاَ يَصْلُحُ إِلاَّ بِالذَّهَبِ".
Abdullah ibn Sinan asked Abu Abdullah عليه السلام about buying silver that contains mercury and lead with silver coins, knowing that when it is melted, it decreases by two or three dirhams for every ten. Imam عليه السلام said: "It is not permissible, except with gold."
- Ṣaḥīḥ al-Faqīh, p. 247