It is narrated from Sayyiduna Abu Waqid al-Laythi (may Allah be pleased with him) that "the Messenger of Allah (peace and blessings be upon him) led the lightest prayer of all people when leading the people, and prayed the longest prayer of all people in his own (private) prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3300