Sahih Muslim
Sahih Muslim 619 a
It is recommended to pray Zuhr at the beginning of its time when there is no intense heat
Arabic hadith text
وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو الأَحْوَصِ، سَلاَّمُ بْنُ سُلَيْمٍ عَنْ أَبِي إِسْحَاقَ، عَنْ سَعِيدِ بْنِ وَهْبٍ، عَنْ خَبَّابٍ، قَالَشَكَوْنَا إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم الصَّلاَةَ فِي الرَّمْضَاءِ فَلَمْ يُشْكِنَا .
Translation
Khabbab reported
We complained to the Messenger of Allah (ﷺ) (the difficulty of) saying prayer on the intensely heated (ground or sand), but he paid no heed to our complaint.