It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "When one of you leads people in prayer, he should keep the prayer short, for among them are the sick, the old, the weak and the young. And when he prays alone, let him pray as he wishes."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5276