“Muhammad ibn al-Hassan once wrote to abu Muhammad (a.s.), asking, ‘A man has hired another man to work and build a structure for another person and he gives the worker food, cotton and other things; then the prices of food and cotton rise or fall and change from the day he gave him, if he can count on him with the price of the day of delivery or the price of the day of finalizing the account. He (the Imam) signed the answer, ‘He must pay according to the prices of the day he set mutual conditions (prices, work and so on) if Allah so wills.’ He (the Imam) (a.s.), about the question of goods that one receives and pays food for it without determining prices which then change, signed the answer, ‘Prices are that of the day he has given the food.’”