Gittin 89 - Rumors of Marriage

If a woman was rumored in town to be betrothed, she is treated as though she were betrothed, that is, she may not marry anyone except the man to whom she is rumored to be betrothed, unless he gives her a Get.

A rumor of marriage is recognized not by mere gossip, but when they say "We heard the rumor from so-and-so, and they heard it from so-and-so" and the court continued to investigate until they find two qualified witnesses who saw the betrothal feast and heard people say "So-and-so was betrothed today."