thrown off a cliff??

I saw a fanart video about mydei which showed him as a baby, and his father throwing him off a cliff. I hadn't seen this in the lore, but I know there's that story about ancient Spartans throwing kids they didn't want off cliffs, so I figured it was based off of that. But today I saw a lore discussion mentioning him being thrown off a cliff as a kid? Is this canon, and if so where is it said? (I thought I collected all the mydei lore in existence already...)