عَنْ عَائِشَةَ زَوْجِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ وَرَضِيَ اللَّهُ عَنْهَا قَالَتْ: كَانَ أَوَّلَ مَا افْتُرِضَ عَلَى رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ الصَّلَاةُ رَكْعَتَانِ رَكْعَتَانِ إِلَّا الْمَغْرِبَ فَإِنَّهَا كَانَتْ ثَلَاثًا ثُمَّ أَتَمَّ اللَّهُ الظُّهْرَ وَالْعَصْرَ وَالْعِشَاءَ الْآخِرَةَ أَرْبَعًا فِي الْحَضَرِ، وَأَقَرَّ الصَّلَاةَ عَلَى فَرْضِهَا الْأَوَّلِ فِي السَّفَرِ
The wife of the Messenger, Sayyidah Aisha (may Allah be pleased with her), says: The prayer that was initially made obligatory upon the Messenger of Allah (peace and blessings be upon him and his family) was two rak'ahs each, except for Maghrib, which was three rak'ahs. Then Allah Almighty completed the prayers of Dhuhr, Asr, and Isha to four rak'ahs each in residence, and the initially prescribed (two rak'ahs) were fixed for travel.