This material is obtained from a Hellfire Shard, Teostra. You can find this monster in Master Rank, so you will have to venture into the Sunbreak campaign, until you find a Teostra. But in case you don't find it, we recommend you to activate any mission available in Elgado Outpost or level up your master rank.
When you're able to take on the Teostra, we recommend looking for the material as the objective reward, which is a 30 percent and 31 percent chance to get it, respectively. Although you can also kill the monster and cut your body or tail to get it, although cutting the thing will be difficult, but you can use a cutting weapon.
Do not seek to capture it because it will not drop what you are looking for, so face it and kill it, it will be the best way to obtain this resource.
If you already have everything clear about where to find a fragment of hellfire in Monster Hunter Rise Sunbreak, we invite you to go for this resource now, so that you can get a lot of use out of it in this expansion.