When the heat is violent, offer (the Zuhr) prayer when it becomes fairly cool, for the violent heat comes from the bubbling over the Hell. (Using translation from Abū Dāʾūd 402)
"إِذَا اشتدَّ الحرُّ فأبْرِدُوا عنِ الصَّلاةِ، وفي لفظٍ بالصلاةِ فإنَّ شدَّةَ الحر من فَيحِ جهنَّم" .