I'm looking for a story about a witch mother.

Hello, a long time ago I saw someone else ask here about a story where a witch mother cast a spell on her son to prevent him from masturbating, but the boy's sister, who is also a witch, uses her magic to make him ejaculate, and in the end, due to the combination of the two spells, the boy's testicles explode. Does anyone know where I can find this story?