Tom Buchanan never tells George Wilson outright that it was Gatsby who was responsible for Myrtle's death.  However, Tom does tell the police, in front of Wilson, that "[Wilson] says he knows the car that did it.... It was a yellow car," and Tom reassures Wilson that the yellow car is not his and that he hasn't seen it all afternoon (one truth and one lie).  This conversation takes place on page 140 of the Scribner edition.  

Further, we know that Tom believes that Gatsby was responsible for Myrtle's death because, on page 141, he says to Nick, "The God damned coward! [...] He didn't even stop his car."  Nick also tells us later, on page 156, that at "about three o'clock the quality of Wilson's incoherent muttering changed—he grew quieter and began to talk about the yellow car.  He announced that he had a way of finding out whom the yellow car belonged to." Wilson seems to jump to the conclusion that the person who hit Myrtle with their car was the same person who sent her home "with her face bruised and her nose swollen" a few months back (156, 157).  Moreover, when Wilson talks about the dog leash with Michaelis, he says, referring to Myrtle's lover (the lover who is still, at this point, known only to Wilson as the man who owns the yellow car), "Then he killed her....  He murdered her." (158)  

In the end, Tom never tells Wilson that Gatsby killed Myrtle, but he initiates the line of thought that ends with this conclusion because it is the conclusion that Tom himself has drawn.

We do not have a page number for this because we do not see the scene in which Tom tells Wilson who was driving the car, or at least, who he thinks was driving the car.  We learn from Nick almost at the end of the story that Tom told Wilson when Nick asks him directly.  He claims that Wilson came to their house while they were preparing to leave and threatened to force his way in. He had a gun. It is at this point that he told Wilson that it was Gatsby's car.  Speaking of Gatsby, he says, "'That fellow had it coming to him.... He ran over Myrtle like you'd run over a dog...'" (187).  In spite of Tom's responsibility in all of this, Nick shakes hands with him, realizing that Tom and Daisy and their kind were not capable of being any other than what they were, so it was pointless to try to change them. It is very shortly after this that Nick leaves to go back to the midwest, a sadder but wiser man.