Hukat 

חקת

Aaron’s death was without prior illness or suffering; it took place calmly, under the direction of God. Moses, too, desired a pleasant death like that, and was granted his wish. 

“The Lord spoke to Moses and Aaron…. Take Aaron and Elazar his son, and take them up Hor Mountain. Undress Aaron of his vestments, and dress Elazar his son in them; Aaron will be gathered, and die there. Moses did as the Lord commanded” (Numbers 20:23–27). This serves to teach you that even though God told Aaron of the harsh decree against him, he did not delay Moses from acting. “Undress Aaron of his vestments.” Moses removed a priestly vestment from him and dressed Elazar in it, and likewise the second vestment, and likewise the third. Moses told Aaron: Enter the cave, and he entered the cave. Moses told him: Climb onto the bed and extend your hands, and he [climbed onto the bed and] extended his hands. Moses told him: Close your mouth, and he closed it. Moses told him: Close your eyes, and he closed them. At that moment, Moses said: Happy is one who dies with this death. Therefore it is stated when Moses was to die: “As Aaron your brother died” (Deuteronomy 32:50) – the death that you coveted. <source>(Yalkut Shimoni, Hukat 1:764) </source>