as told by Joseph Telushkin in Jewish Humor
When the nineteenth century Hasidic rebbe Levi Yizchak of Berditchev
sent out invitations to his son's wedding, he wrote that it would
take place in Jerusalem on such-and-such a date and time, but
"if, G-d forbid, the Messiah has not yet arrived, then the wedding
will be held on the same date and time here in Berditchev."