This sound effect can be found on the SFX Kit, which was made by Sound Ideas. It is a low pitched, modified version of Hollywoodedge, Elephant Single Clas AT043901.
Links:
https://sounddogs.com/Search?RecordingType=Sound%20Effects%20and%20Music&NavSearch=True&keywords=10239057
https://soundeffects.fandom.com/wiki/Sound_Ideas,_MONSTERS_%26_CREATURES_%5C_BEASTS_-_EXTRA_LARGE_MONSTER:_GIANT_LIZARD:_ROAR_02#Audio_Samples
