Language:
كتاب الأذان
10  
Call to Prayers (Adhaan)
(61)
Chapter: The shortening of the Qiyam (standing) by the Imam[in Salat (prayer)] but performing the bowings and the prostrations perfectly
(61)
باب تَخْفِيفِ الإِمَامِ فِي الْقِيَامِ وَإِتْمَامِ الرُّكُوعِ وَالسُّجُودِ
Sahih al-Bukhari 702

Narrated Abu Mas`ud:

A man came and said, "O Allah's Messenger (ﷺ)! By Allah, I keep away from the morning prayer only because So and so prolongs the prayer when he leads us in it." The narrator said, "I never saw Allah's Apostle more furious in giving advice than he was at that time. He then said, "Some of you make people dislike good deeds (the prayer). So whoever among you leads the people in prayer should shorten it because among them are the weak, the old and the needy."

حَدَّثَنَا أَحْمَدُ بْنُ يُونُسَ، قَالَ حَدَّثَنَا زُهَيْرٌ، قَالَ حَدَّثَنَا إِسْمَاعِيلُ، قَالَ سَمِعْتُ قَيْسًا، قَالَ أَخْبَرَنِي أَبُو مَسْعُودٍ، أَنَّ رَجُلاً، قَالَ وَاللَّهِ يَا رَسُولَ اللَّهِ إِنِّي لأَتَأَخَّرُ عَنْ صَلاَةِ الْغَدَاةِ مِنْ أَجْلِ فُلاَنٍ مِمَّا يُطِيلُ بِنَا‏.‏ فَمَا رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم فِي مَوْعِظَةٍ أَشَدَّ غَضَبًا مِنْهُ يَوْمَئِذٍ ثُمَّ قَالَ ‏ "‏ إِنَّ مِنْكُمْ مُنَفِّرِينَ، فَأَيُّكُمْ مَا صَلَّى بِالنَّاسِ فَلْيَتَجَوَّزْ، فَإِنَّ فِيهِمُ الضَّعِيفَ وَالْكَبِيرَ وَذَا الْحَاجَةِ ‏"‏‏.‏
Reference : Sahih al-Bukhari 702
In-book reference : Book 10, Hadith 97
USC-MSA web (English) reference : Vol. 1, Book 11, Hadith 670
  (deprecated numbering scheme)