Al-Kāfi - Volume 5 > Selling Arms to al- Sultan
Hadith #4

4- أَحْمَدُ بْنُ مُحَمَّدٍ عَنْ أَبِي عَبْدِ اللهِ الْبَرْقِيِّ عَنِ السَّرَّادِ عَنْ أَبِي عَبْدِ اللهِ (عَلَيْهِ السَّلام) قَالَ قُلْتُ لَهُ إِنِّي أَبِيعُ السِّلاحَ قَالَ لا تَبِعْهُ فِي فِتْنَةٍ.

4. Ahmad ibn Muhammad from abu ‘Abd Allah al-Barqiy from al-Sarrad who has said the following: “I once said to abu ‘Abd Allah, ‘Alayhi al-Salam, that I sell arms. He (the Imam) said, ‘You must not sell them in times of mischief.’”