Language:
كتاب الأذان
10
Call to Prayers (Adhaan)
(62)
Chapter: When offering Salat (prayer) alone, one can prolong the Salat as much as one wishes
(62)
باب إِذَا صَلَّى لِنَفْسِهِ فَلْيُطَوِّلْ مَا شَاءَ

Narrated Abu Huraira:

Allah's Messenger (ﷺ) said, "If anyone of you leads the people in the prayer, he should shorten it for amongst them are the weak, the sick and the old; and if anyone among your prays alone then he may prolong (the prayer) as much as he wishes. "

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، قَالَ أَخْبَرَنَا مَالِكٌ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ إِذَا صَلَّى أَحَدُكُمْ لِلنَّاسِ فَلْيُخَفِّفْ، فَإِنَّ مِنْهُمُ الضَّعِيفَ وَالسَّقِيمَ وَالْكَبِيرَ، وَإِذَا صَلَّى أَحَدُكُمْ لِنَفْسِهِ فَلْيُطَوِّلْ مَا شَاءَ ‏"‏‏.‏
Reference : Sahih al-Bukhari 703
In-book reference : Book 10, Hadith 98
USC-MSA web (English) reference : Vol. 1, Book 11, Hadith 671
  (deprecated numbering scheme)