cellio | daf bit: Yevamot 117

The mishna discusses a case of unproven death: if a man and a woman move across the sea and there is peace between them (they're a happy couple) and there is peace in the land, and she returns home and reports that her husband is dead, she is believed and she may remarry. If either of those conditions isn't true she isn't believed. (This is from 114b and I supply it for context.)

Now what happens if there are witnesses (besides the wife) and they disagree? If one witness said he is dead and on that basis she was allowed to remarry, and then another witness comes and says he is alive, she is not required to divorce. But if one said he is dead and two say he is alive, then even though she remarried legally, she must divorce. And if two said he is dead and one said he is alive, she needn't divorce and may remarry if she hasn't yet. (117a-b)

(In case you're wondering what peace in the land has to do with anything: the g'mara points out that in time of war people may come to incorrect conclusions if people don't return.)