Fixing the profit in a sale at one-third

Question:
The first questioner says: I hear what is circulating among the common people, and perhaps among some who claim to be students of knowledge, that if you buy a commodity and want to sell it, it is not permissible for you to take a profit of more than one-third. Is there any evidence for this?

Answer:
As for this meaning of fixing the profit, it is that he sells it for what Allah has made easy and what he profits from. However, if he reduces it and shows leniency to his brother, taking only a small profit, that is better. Otherwise, fixing the profit is not a condition. It is known that the honest person is the one who makes things easy; he does not fix the profit. The Prophet (peace and blessings be upon him) bought a camel...