Recently on Hockey Night in Canada, host Ron Maclean told viewers a little story about how Maurice Richard asked to change his number from 15 to 9 during the 1942-43 season in honour of his new baby girl Hugette, who weighed in at 9 pounds.
Wikipedia also says the same thing. Along with everywhere else you look.
But the number 9 must have already held a soft spot in Rocket’s heart, because as you can see in the lineup below, he was wearing it when he was playing senior hockey, a year before he joined the big club.