Isru Chag in the Land of Israel and the second day of Shavuot in the diaspora
1096- Rabbeinu Tam is stabbed five times during a pogrom in Ramerupt, France and is miraculously saved by a passing knight.
1749- Yahrtzeit of the ger tzedek Avraham ben Avraham, Count Valentine Potocki killed in Vilna. Avraham ben Avraham, the famed "Ger Tzedek" (Righteous Convert) of Vilna, was born as Valentin Potozki, the son of Count Potocki, one of the richest landowners in Poland. As a student in Vilna he discovered Judaism and decided to convert -- a capital offense in most countries in Christian Europe at the time.
He fled to Amsterdam where he secretly converted to Judaism, assuming the name Avraham ben Avraham ("Abraham the son of Abraham"). Years later he returned to Vilna, where he was eventually recognized as the missing son of Count Potocki and arrested by the church. He refused to renounce his faith and was sentenced to death. He was burned at the stake in Vilna on the 2nd day of Shavuot of 1749.