"Yabba-dabba-doo!" is the catchphrase of Fred Flintstone on The Flintstones, usually to express exuberance and astonishment. Alan Reed, the original voice of Fred Flintstone, came up with the term ad lib during an early recording session for the series; as Joseph Barbera recalls it in his 1994 memoir My Life In Toons, Reed noted that the script called for him to say simply "Yahoo!", but felt that "Yabba-dabba-doo!" might make it more interesting.

Source: Fandom