مُوَطَّأُ مَالِكٍ
Muwatta Malik 2
The Times of Prayer
قَالَ عُرْوَةُ وَلَقَدْ حَدَّثَتْنِي عَائِشَةُ زَوْجُ النَّبِيِّ صلى الله عليه وسلم أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يُصَلِّي الْعَصْرَ وَالشَّمْسُ فِي حُجْرَتِهَا قَبْلَ أَنْ تَظْهَرَ .
Urwa said that A'isha, the wife of the Prophet, (ﷺ) used to pray asr while the sunlight was pouring into her room, before the sun itself had become visible (i.e. because it was still high in the sky).
Arabic/English book reference: Book 1, Hadith 2