وَحَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، حَدَّثَنَا الْمُغِيرَةُ، - وَهُوَ ابْنُ عَبْدِ الرَّحْمَنِ الْحِزَامِيُّ - عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ ‏"‏ إِذَا أَمَّ أَحَدُكُمُ النَّاسَ فَلْيُخَفِّفْ فَإِنَّ فِيهِمُ الصَّغِيرَ وَالْكَبِيرَ وَالضَّعِيفَ وَالْمَرِيضَ فَإِذَا صَلَّى وَحْدَهُ فَلْيُصَلِّ كَيْفَ شَاءَ ‏"‏ ‏.‏

Abu Huraira reported: The Apostle of Allah (PBUH) said: When any one of you leads the people in prayer, he should be brief for among them are the young and the aged, the weak and the sick. But when one of you prays by himself, he may (prolong) as he likes. Translation Not Available

Book Ref: Sahih Muslim Book 4 Hadith 942
Web Ref:  Sahih Muslim Book 4 Hadith 467 a