It's chapter 400, page 7.
Yeah but you're missing the point lol. Yeah it never would have happened if he didn't invade, But Tobi's intentions was not to destroy the Leaf, nor did he expect Minato to take it from him. Soo, in actuality, the Leaf wasn't in danger of being totally destroyed until Minato took it from his control. Minato's act of freeing it from Tobi is what put the the village at risk of annihiliation, buuuut, he did fix that on his own. But that has little to do with Tobi. And Yeah they had many ninja to defend, but it wasn't Tobi's plans to kill them all.
I doubt that would have done any good, Danzo and the elders would have come to the conclusion that it was an Uchiha in a mask, even Minato wasn't 100% sure....
Minato was the youngest Hokage ever, Danzo and the elders wouldn't have given any more consideration than they would have Sarutobi. Sarutobi on the other hand..he was well respected (Though every Hokage was respected, Minato wasn't noted for anything other than dying for the village and all he did right before his death), and had lots of experience as Hokage, but yet was still forced to let the massacre go through. To add even more, the elders were on the same team as Sarutobi, and showed respect for him even then. Sarutobi had great influence, and to add even MORE, you yourself say that "He's repsonsible for bringing tthe Leaf to it's prime."
Now, Minato... what, because he appears to be wise? Wiser than Sarutobi? Has more influence than Sarutobi? Or is it just because FTG beats everything? -__- He can't do everything, he himself said that he doesn't have the answer on how to end hatred or pain (can't remember which) within the ninja world. He couldn't have done squat to prevent the massacre.