(a) It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that he (peace and blessings be upon him) said: "When one of you leads people in prayer, he should make it light, for among them are the sick, the weak and the old; and when you pray by yourself, make it as long as you wish."
(b) In the narration of Imam al-Shafi'i (may Allah have mercy on him), the Messenger of Allah (peace and blessings be upon him) said: "When one of you leads people in prayer, he should make it light, for among them are the sick and the weak; and when he prays by himself, let him make it as long as he wishes."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5275