Alcohol and breastfeeding

So I have a 4 week old son I'm breastfeeding and I rarely ever drink to begin with and haven't had any drinks for 10 months now and went to lunch with some family and had a tall glass of beer could been close to two beers I'm not sure was tall and anyways I'm so worried if my son will be safe to drink my milk now do you think he would be alright or should I pump it out and throw it away and how many times till it's out of my system I know this might seem dumb I'm a FTM though and just worry I don't want anything to happen to him