One day Imam Sadiq (as) gave 1000 dirham to one of his servants to do business on his behalf. Musadif, the Imam's servant, bought merchandise, went to Egypt, and after selling his goods came back to the Imam (as) with 2000 dirham.
Imam Sadiq (as) gave 1000 dirham to Musadif, one of his servants, and said to him,
Get ready for a journey to Egypt and buy goods with this money to be sold in Egypt. I have so many people dependent on me for sustenance.
After purchasing the merchandise, Musadif set off for Egypt. Near Egypt, their caravan saw a group of merchants returning from Egypt. After inquiring them, Musadif and his companions realized that their merchandise was scares in Egypt and thus, expensive. They made an agreement and took an oath to not sell their merchandise for less than twice its purchasing price.
As a result, Musadif could sell his merchandise for twice its purchasing price. After coming back from Egypt, he went to Imam Sadiq (as) and put two bags of money, each containing 1000 dirham, in front of the Imam (as) and said,
May I be sacrificed for you! One of them is the original 1000 dirham you gave me, and the other is another 1000 dirham I the profit I made.
The Imam asked how he had made such huge profit and Musadif told the Imam (as) the story. Imam Sadiq (as) said,
Praise be to God! You made an oath against Muslims to sell your good to them for twice its purchasing price?!
The Imam then took one of the bags and said,
This is the original money I gave you. As for the other bag, I have nothing to do with it. I don’t want such profit.
The Imam (as) added,
O Musadif! Fighting in the battlefield is easier than earning halal income!
Reference: Al-Kafi, vol. 5, p. 162