Sunan Abi Dawud Book 2, Hadith 405
when one of you leads the people in prayer, he should be brief, for among them are the sick, the aged and the needy.
When one of you leads the people in prayer, he should be brief, for among them are the weak, the sick, and the aged. But when one of you prays by himself, he may pray as long as he likes.
I heard the apostle of Allah (ﷺ) say: A man returns after saying his prayer while a tenth part of his prayer, or a ninth part, or an eight part, or a seventh part, or a sixth part, or a fifth part, or a third part, or half of it, is recorded for him.