waking baby for feedings

kentucky_mommy
My little boy is 12 weeks old and he's starting to sleep through the night, he'll sleep from around 11:30-6:45 and then he'll wake up to eat. But my mom keeps him over night sometimes and she wakes him up at 4 in the morning to eat both times she's kept him. She told me I need to wake him up to eat cause I'm starving him but I've always heard that as long as he's gaining weight and eating good to let him sleep that he'll wake up when he's hungry. Which is the right thing? He's almost 14 pounds. 7.07 lbs at birth.