Related for Gittin 151:18

A man who said to a woman: "Behold you are betrothed to me with the understanding that I will talk to the ruler about you"; "[With the understanding that] I will work as a labourer with you", and he gave her something worth a perutah—she is betrothed immediately [even if he hasn't fulfilled his condition yet], until he says "I didn't speak [to the ruler]" or "I didn't work [as a labourer]" [when she becomes retroactively never betrothed]—words of Rabbi Meir. But Hakhamim say: If the stipulation is fulfilled—she is betrothed; but if not—she is not betrothed. (But see Lieberman who thinks this is about tenai kaful.) Rabban Shimon ben Gamliel says: There is no [valid] stipulation in the ketubah that isn't doubled (tenai kaful, that explains what would happen both if he did the thing he promised and also if he didn't do it).