The PM says Labour's London mayoral candidate Sadiq Khan has "appeared again and again and again" on a platform with an IS supporter.
In a noisy chamber, and amid claims of "disgraceful" from Jeremy Corbyn, David Cameron said: "They are shouting down this point because they don't want to hear the truth."
He was responding to a question from Conservative MP Christopher Pincher who asked about condemning extremists and sharing a platform with them.