Sahih Al Bukhari (543)

عن أنس بن مالك قال {لم يخرج النبي صلى الله عليه وسلم ثلاثا فأقيمت الصلاة فذهب أبو بكر يتقدم فقال نبي الله صلى الله عليه وسلم بالحجاب فرفعه فلما وضح وجه النبي صلى الله عليه وسلم ما نظرنا منظرا كان أعجب إلينا من وجه النبي صلى الله عليه وسلم حين وضح لنا فأومأ النبي صلى الله عليه وسلم بيده إلى أبي بكر أن يتقدم وأرخى النبي صلى الله عليه وسلم الحجاب فلم يقدر عليه حتى مات}

Anas (may Allah be pleased with him) narrated the Prophet (peace be upon him) did not come out for three days. The people stood for the prayer and Abu Bakr went ahead to lead the prayer. (In the meantime) the Prophet (peace be upon him) caught hold of the curtain and lifted it. When the face of the Prophet (peace be upon him) appeared we had never seen a scene more pleasing than the face of the Prophet (peace be upon him) as it appeared then. The Prophet (peace be upon him) beckoned to Abu Bakr to lead the people in the prayer and then let the curtain fall. We did not see him (again) until he died.