The slogan most frequently associated with Superman is "Truth, justice and the American way." However, he does not always say it in every piece of media the character appears.
In fact, when Superman was first adapted to the screen in the Max Fleischer cartoons that ran starting in 1941, he was said to be fighting "a never-ending battle for truth and justice." In his first live-action appearance, the 1948 serials starring Kirk Alyn, Superman's father instructs him to use his powers "in the interests of truth, tolerance and justice."
It wasn't until Superman's first television appearance in 1950 that the phrase "truth, justice and the American way" was used in visual media. The phrase originates from the "Adventures of Superman" radio series, which began airing in 1940.