With the hope of receiving a reply with proof....

There is absolutely no way a 3 month old is potty trained. As in, the 3 month old infant can communicate and use a toilet. They likely can't even hold their head up at that age.

https://www.babycenter.com/baby/diapering/infant-potty-train... indicates that a potty can be introduced from 4- to 6-months old. Potty trained by 18 months is much more reasonable.