"Assassin of the Moonlit Night" (月夜の暗殺者, Tsukiyo no Ansatsusha) is episode 76 of the original Naruto anime.
Seeing Naruto and Sakura's determination to protect Sasuke, Gaara remembers his childhood with his uncle Yashamaru. They talked about pain — with Yashamaru explaining to him that the pain dealt to the heart takes the longest to heal and the only cure to such wound is love. Gaara, in time made a deep bond with him feeling the pain going away with Yashamaru's love. One night, after he killed a drunk while Gaara was lost in deep thoughts, an assassin attacked him from behind. Gaara's sand protected him as always and he attacked the assassin. When Gaara went on to check the person behind the mask, he was shocked to see it was Yashamaru.