The Yerushalmi (Bikkurim 3:3/11b) says that a chassan has his sins atoned for. This is derived from Esav, who married a woman, the daughter of Yishmael and sister of Navos, named Machalas (Bereishis 28:9). Now, another wife of Esav's who is the daughter of Yishmael and sister of Navos is named Basmas (Bereishis 36:3) and is presumably the same person. Why, then, is she called Machalas in our passuk? Because on her account, Esav's sins were atoned for (nimchalu).
This drashah is kind of crazy if you think about it. Esav was a murderer (Rashi to Bereishis 25:29) and an idolater (Rashi to Bereishis 27:1, first explanation). And yet you say that getting married just wipes that all away? Also, this wasn't even his first wife; he had previously married Adah and Oholibamah (Bereishis 26:34). Yet it's still an atonement for him?
How can it be that one is able to spend his days doing horrendous sins and his nights getting married and he'll get a free pass into Olam Haba?
I suppose an easy answer is that it's just an asmachta, but I'd really like it if someone could find a source that actually makes the drasha work.