What is the ruling on one who speaks during the Friday sermon – such as by motioning for silence, for example – is his prayer valid, or must he repeat the Dhuhr prayer?

Whoever alerts another to abandon idle talk during the sermon has engaged in idle talk, according to the Prophet's (peace be upon him) saying: "If you say to your companion on Friday, 'Be silent,' while the Imam is delivering the sermon, then you have engaged in idle talk." This idle talk does not invalidate the Friday prayer, but it diminishes its reward. The Friday prayer remains valid, and the person is not required to repeat it or perform the Dhuhr prayer.