Season 9: Episode 193: The One Where No One Proposes
Joey tries to tell Rachel that he didn't really propose, but can't get a moment alone with her. Phoebe gets involved but that just confuses things. Joey tries to keep Ross away from Rachel until he can straighten it out. Monica and Chandler continue trying to get pregnant; Mr. Geller discovers them having sex in the janitor's closet and is mortified, until he learns that they're trying to conceive; then he's so enthusiastic he starts giving them advice, and Monica is mortified. Joey, Ross, and Rachel finally straighten out that no one was going to propose; Ross was just planning to ask Rachel if they could start up their relationship again. Everything is just about smoothed out when Ross realizes that Rachel is wearing the ring, and therefore must have said yes to Joey.