Yahya related to me from Malik from Abu'z Zinad from al-Araj fromAbu Hurayra that the Messenger of Allah, may Allah bless him and granthim peace, said, "When you lead people in the prayer, make it short,because there are among them some people who are weak, ill and old.But when you pray on your own, make it as long as you wish."
App reference: Book 8, Hadith 14
USC-MSA web (English) reference: Book 8, Hadith 14
Arabic reference: Book 8, Hadith 303