Full Sharh — Bulugh al-Maram 525
وَعَنْ أَنَسٍ: { كَانَ رَسُولُ اَللَّهِ - صلى الله عليه وسلم -إِذَا اِرْتَحَلَ قَبْلَ أَنْ تَزِيغَ اَلشَّمْسُ أَخَّرَ اَلظُّهْرَ إِلَى وَقْتِ اَلْعَصْرِ, ثُمَّ نَزَلَ فَجَمَعَ بَيْنَهُمَا, فَإِنْ زَاغَتْ اَلشَّمْسُ قَبْلَ أَنْ يَرْتَحِلَ صَلَّى اَلظُّهْرَ, ثُمَّ رَكِبَ } 1 مُتَّفَقٌ عَلَيْهِ.1 - صحيح. رواه البخاري (2/582-583)، ومسلم (704).
English Translation
Narrated Anas (RA):: When Allah's Messenger (ﷺ) (while on a journey) proceeded before the sun had declined from the centre of the sky, he (ﷺ) delayed the Zuhr prayer till the time of the 'Asr prayer; he (ﷺ) would then alight and combine the two prayers. If the sun declined before he (ﷺ) moved off, he (ﷺ) would offer the Zuhr prayer and ride (i.e. travel). .
Source
Bulugh al-Maram(بلوغ المرام)
The Book of Prayer
Hadith Number
525