"Assassin of the Moonlit Night" (月夜の暗殺者, Tsukiyo no Ansatsusha) is episode 76 of the original Naruto anime.
Seeing 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 his uncle, feeling the pain going away with Yashamaru's love. One night, after he accidentally killed a drunk who looked at Gaara as if he was a monster, Gaara was attacked from behind by an assassin. Gaara's sand protected him as always and he in turn attacked the assassin. After taking out the assassin, Gaara went to check on his attacker's identity, shocked to discover that it was none other than Yashamaru.
In the present, Naruto is now standing in front of Sasuke, ordering Gaara to let her go. When Gaara asks who Sasuke and Sakura are to him, he states that they are his friends, and that he will pulverize Gaara if he continues to hurt them. Gaara responds by hurting Sakura, and asks why Naruto hasn't pulverized him yet; Naruto clenches his fists and rushes towards Gaara.