It is narrated from Sayyiduna Samurah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you becomes drowsy on the day of Jumu'ah while the imam is delivering the sermon, let him get up from his place and seat his brother in his place."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6926