Where does it show in the bible that smoking weed a sin?

Pot smokers have been saying for years now that smoking marijuana is in The Bible. I have heard so many things but the most popular is this: "And on the fourth month and 29th day, they smoked." I haven't been able to find that ANYWHERE. But here's the real question: Where does it say that it is wrong? Opium was around in those times yet it has never been mentioned that you should never smoke it. At least not the bible I have. Hope this helps.