Arakhin 6B

איני? והא רבי ינאי יזיף ופרע! שאני רבי ינאי, דניחא להו לעניים דכמה דמשהי מעשה ומייתי להו.

The Talmud asks: Is that so? But R' Yannai, who was a charity collector, borrowed money belonging to charity and repaid. The Talmud answers: The case of R' Yannai is different; it is beneficial to the poor that he be allowed to borrow and repay, as the longer he leaves the charity fund empty, the more he impels people to give charity, and he thereby brings more money to the poor.

תנו רבנן: ישראל שהתנדב מנורה או נר לבית הכנסת ⁠— אסור לשנותה. סבר רבי חייא בר אבא למימר: לא שנא לדבר הרשות ולא שנא לדבר מצוה. אמר ליה רב אמי: הכי אמר רבי יוחנן ⁠— לא שנו אלא לדבר הרשות, אבל לדבר מצוה מותר לשנותה.

A baraita states a baraita that deals with a similar matter: In the case of a Jew who donated a candelabrum or a lamp to the synagogue, it is prohibited to change it and use it for another purpose. R' Ḥiyya bar Abba thought to say that there is no difference whether he wishes to change for a voluntary matter or for a matter involving a mitzva, as in both cases it is prohibited. Rav Ami said to R' Ḥiyya bar Abba: This is what R' Yoḥanan says: When A baraita states the baraita, they taught only that it is prohibited when he changes it for a voluntary matter, but it is permitted to change it for a matter involving a mitzva.

מדאמר רבי אסי אמר רבי יוחנן: גוי שהתנדב מנורה או נר לבית הכנסת, עד שלא נשתקע שם בעליה ⁠— אסור לשנותה, משנשתקע שם בעליה ⁠— מותר לשנותה.

This halakha is derived from the fact that R' Asi says that R' Yoḥanan says: With regard to a non-Jew who donated a candelabrum or a lamp to the synagogue, if it is before its owner’s name has been forgotten, i.e., people still remember that he donated the item, it is prohibited to change it and use it for another purpose. Once its owner’s name has been forgotten, it is permitted to change it.