Bava Kamma 20B

הא איתהנית!

You have derived benefit from my property, as by living there you saved the money you otherwise would have had to pay in order to rent out a different courtyard, and therefore you must pay me for the benefit you derived.

אמר ליה: מתניתין היא. הי מתניתין? אמר ליה: לכי תשמש לי. שקל סודריה כרך ליה. אמר ליה: אם נהנית ⁠– משלמת מה שנהנית.

Rami bar Ḥama said to him: This dilemma is not new; rather, it is discussed in the Mishnah, and the Mishnah already provided a solution. Rav Ḥisda asked him: To which Mishnah are you referring? Rami bar Ḥama said to him: After you serve me, I will tell you. Rav Ḥisda took hold of Rami bar Ḥama’s scarf [suderei] and folded it, as an act of service. Rami bar Ḥama then said to him: This is the Mishnah: If the animal derives benefit, the owner of the animal pays for the benefit that the animal derived. This demonstrates that one who derives benefit must pay for the benefit he derives, even if the injured party is not entitled to payment for his loss.

אמר רבא: כמה לא חלי ולא מרגיש גברא דמריה סייעיה ⁠– דאף על גב דלא דמי למתניתין, קבלה מיניה. האי זה נהנה וזה חסר, והאי זה נהנה וזה לא חסר הוא!

Rava said: How little does a man who has the assistance of his Lord have to worry or be concerned about the possibility that his opinion may not be accepted, as even though the dilemma that was raised is in fact not similar to the case in the Mishnah quoted by Rami bar Ḥama, Rav Ḥisda nevertheless accepted it from him. This case in the Mishnah, about the animal eating produce in the public domain, is where this one derives benefit and that one suffers a loss, and that case of the squatter living in the courtyard, is where this one derives benefit and that one does not suffer a loss.