From: Anecdotes of the Pious Ones, # 43, V. 1

That day Sulaiman bin Ja'far Ja'fary had been out for some duty with Imam Ridha (as). When night was approaching, and Sulaiman wanted to go home, the Imam (as) invited him to his place for dinner. He accepted.

Imam noticed that the servants were busy with some project. Meanwhile, he noticed a new face in the crowd. He wondered who that was.

The servants said: "We hired him today."

"Very well. How much are you paying him?"

"We will give him something and make him happy."

Signs of disapproval appeared on the Imam's face.

Sulaiman interjected and said: "Don't bother yourself, please."

Imam (as) said: "I have told them, repeatedly, that they should never make a commitment, unless the price is set. That they should never hire somebody unless they set the wages. You should always determine the wage, then ask the person to work. If you choose to give him more than his wages, he would be thankful. He will like the gesture, and your relationship will foster. And if you give him the amount promised, he will not be upset. However, if you don't determine the wages, and make him work, whatever you give him at the end of the work, he shall not know that you have been generous with him. He might suspect that you have given him less than he deserves." [1]

[1] Bihar al-Anwar, V 12, p. 31