Dragon Ball Z - episode 43 - 10 Apr, 1990

Gohan, Krillin, and Bulma are one Dragon Ball away from making their wish. But during their search for the seventh Dragon Ball, their two Namekian friends reveal that they are not Namekians at all. In fact, they're not even on Namek. Meanwhile, Vegeta learns that Frieza has traveled to Namek to gather the Dragon Balls. Not wanting to be beaten to the punch, Vegeta immediately blasts off for Namek. (Source: Wikipedia)