Sahih al-Bukhari 703
صحيح البخاري#703SahihNarrated 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 you prays alone then he may prolong (the prayer) as much as he wishes
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 10:98