The Wedding - S1-E12
Plot hole: After Claudia's call, they decided that Lilly will meet her at the bar and the guys will meet Stuart. They're all at the apartment at the same time and the dudes have gotten to Stuart's apartment, convinced him to still marry Claudia and then go back to the bar right after Lilly gets there. And also giving a lot of time to Barney hitting on Claudia. There's no way that could happen in this order, they live right above the bar, Lilly was supposed to be there before Claudia.
Chosen answer: In a flash forward scene in Season 8, it shows him with his first born: a daughter.
XIII