After Vishnu created Brahma from the lotus upon his navel, he created two drops of water upon the water, which were imbued with the attributes of tamas (darkness) and rajas (activity). Madhu and Kaitabha were born from these drops, whereupon they started to worship Mahadevi, acquiring the boon of dying only when they desired.
Vishnu created Brahma by forming a lotus on his belly, then formed two water beads that embodied the qualities of darkness (tamas) and energy (rajas). Madhu and Kaitabha were born from these droplets, after which they began to honor Mahadevi, acquiring the ability to die at their own whim.