This is from Uncanny X-Men #192, #193, and #196. It's by Chris Claremont and John Romita, Jr.
In #192...
In #193...
In #196, Xavier is teaching his class when he overhears one of his students thinking "We've got no choice-- he knows who we are, he knows what we did-- we've got to kill him!" Since he is still weakened and recovering from the attack, he is unable to probe his students' minds and find the guilty party. He doesn't know it's one of the students who had attacked him.
Xavier gets the X-Men (along with Magneto, who's joined the team) to help prevent the murder. Meanwhile, Rachel runs into the Beyonder (who's pretending to be human) and recognizes his presence from an earlier encounter.
Xavier's attackers plant a trap in his office. Later, Kitty runs into them in the physics lab while she's investigating. When they realize she attends Xavier's private school they try to kill her.