Al-Kāfi
Hadith 194وَ بِهَذَا الْإِسْنَادِ عَنْ أَبِي عَبْدِ اللَّهِ ( عليه السلام ) قَالَ إِنَّا نَأْمُرُ الصِّبْيَانَ أَنْ يَجْمَعُوا بَيْنَ الصَّلَاتَيْنِ الْأُولَى وَ الْعَصْرِ وَ بَيْنَ الْمَغْرِبِ وَ الْعِشَاءِ الْآخِرَةِ مَا دَامُوا عَلَى وُضُوءٍ قَبْلَ أَنْ يَشْتَغِلُوا .
7. Through the same chain of narrators as that of the previous Hadith, the following is narrated: “Abu ‘Abd Allah (a.s.), has said, ‘We instruct children to perform two Salat (prayer) together, one Salat (prayer) soon after the other, like al-Zuhr and al-‘Asr, al-Maghrib and al-‘Isha ’ as long as they have valid wudu before they get busy.’”