The sage R’ Eliezer the son of Jacob ruled: a man should not marry two women who live in different countries, lest their children, not knowing each other though they are half-siblings, meet, fall in love, and form an incestuous marriage. The scholars asked: Was it not the habit of one of the sages, Rav, when he wandered far from home, to publicly announce “Who wants to be my wife for one day”? This was the practice, too, of another sage, Rav Nachman. This implies, the scholars said, that one may marry two women in distant locations, and that we do not fear one’s children will marry each other. Answer: Famous sages may marry women in distant places because their children will be known as children of the famous sage, and so there is no fear they will marry each other. The scholars then asked: How did these sages marry women for a single day? Was it not ruled as law that a woman gets so excited and aroused by a marriage proposal that she menstruates, and one is forbidden to have sexual relations with her for seven days, because a niddah is forbidden to her husband? Answer: These sages would send messengers to make their announcement and offer her marriage seven days before the sages’ arrivals. Another answer: These sages did not have sexual relations with their short-term wives; they only spent time alone with them.
(Babylonian Talmud, Tracate Yevamot 37b)