Xuanmen cultivation involves mastering the five Qi within the chest and the three flowers upon the crown. Once the three flowers gather at the crown and the opportune moment arrives, one can use an Xiantian spiritual treasure to sever the three corpses.
However, Dao Ancestor Hongjun did not use three Xiantian spiritual treasures to sever his three corpses; instead, he used a single Xiantian Supreme Treasure, the Jade Plate of Creation—for not every Xiantian Supreme Treasure is suited to harbor the three corpses.
The Jade Plate of Creation is inherently a Chaos supreme treasure belonging to the Great God Pangu, possessing supreme divine might. To say nothing of using it to harbor the severed corpses, even recreating the world would not be entirely impossible, provided the user's cultivation had reached a sufficient level!
Chapter 80