How I Met Your Mother Season 9 Episode 22
The End of the Aisle
Robin panics at the last minute before her wedding and voices her doubts about marrying Barney to Ted. She admits she hoped Barney would somehow find her locket. Ted gives it to Barney to give to Robin, but she sees through his story. Barney struggles to write his vows and is hesitant to take and advice from Marshall and Lily. He explains how they probably have broken many of their wedding day vows. Marshall and Lily decide to exchange new vows more in keeping with their current life together.
Robin thinks maybe she should have married Ted. When he refuses to run away with her, she flees alone, only to collide with the mother. The mother gives Robin some good advice. Barney finds Robin and tells her his one vow.
Robin finally walks down the aisle and meets Barney at the altar.