Sulayman al-Ja’fari narrates that one day we went with Imam Ali al-Rida (as) to his house. Upon entering the courtyard, we found the servants of the Imam busy at work. The Imam noticed a stranger among his servants. Imam asked: “Who is this man with you?”
The servants replied: “He is helping us in our work and at the end of the day we will give him something as his wages.”
The Imam asked: “Have you talked and agreed with him on his wages?”
The servants replied: “No; but he will be pleased with whatever we will give him.”
The Imam became very angry with his servants. Sulayman al-Ja’fari asked the Imam, “…Why are you taking this issue so hard on yourself?”
The Imam noted: ”I have several times forbidden them from employing anyone to work with them unless they have agreed upon his wages. Know that even if you pay three times more than the average wages to someone who works for you without prior agreement, he will still think that you have underpaid him. But if you have agreed on the wages, and then you pay him that wage, he will thank you for the fulfillment of your agreement; and if you add even a little to it, he will recognize it as your generosity and know that you have paid him more.”
Reference: Furu’ al-Kafi, vol. 1, p. 288 – Translation: Business Ethics in Islam By Sayyid Muhammad Rizvi (2007)