Interest earned on Shabbat

Hi,

A Jew is not permitted to earn money by rental of his property, including his money, on Shabbat or Yom Tov. Therefore, a Jew who receives interest for his funds stored in a bank [in an arrangement such that interest is permitted at all, which is another topic] may not receive payments calculated by the day, if that day is Shabbat or Yom Tov.

This is not a problem on a normal Shabbat or Yom Tov, since the days are calculated from midnight to midnight, and therefore they include non-Shabbat/Yom Tov hours. However, if Friday or Sunday is Yom Tov then there is a midnight-to-midnight period which is prohibited. In such a case, since one cannot practically decline the payment, one should give the relevant sum to tzedakah in a manner in which he will receive no reward at all.

(Rav Moshe Feinstein, Igrot Moshe Orach Chaim 4:59)

Have a great day,
Mordechai