Sahih Bukhari Volume 1, Book 10, Hadith 685

حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، قَالَ حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ أَيُّوبَ، عَنْ أَبِي قِلاَبَةَ، عَنْ مَالِكِ بْنِ الْحُوَيْرِثِ، قَالَ قَدِمْنَا عَلَى النَّبِيِّ صلى الله عليه وسلم وَنَحْنُ شَبَبَةٌ، فَلَبِثْنَا عِنْدَهُ نَحْوًا مِنْ عِشْرِينَ لَيْلَةً، وَكَانَ النَّبِيُّ صلى الله عليه وسلم رَحِيمًا فَقَالَ ‏"‏ لَوْ رَجَعْتُمْ إِلَى بِلاَدِكُمْ فَعَلَّمْتُمُوهُمْ، مُرُوهُمْ فَلْيُصَلُّوا صَلاَةَ كَذَا فِي حِينِ كَذَا، وَصَلاَةَ كَذَا فِي حِينِ كَذَا، وَإِذَا حَضَرَتِ الصَّلاَةُ فَلْيُؤَذِّنْ لَكُمْ أَحَدُكُمْ، وَلْيَؤُمَّكُمْ أَكْبَرُكُمْ

Narrated By Malik bin Huwairth : We went to the Prophet and we were all young men and stayed with him for about twenty nights. The Prophet was very merciful. He said, "When you return home, impart religious teachings to your families and tell them to offer perfectly such and such a prayer at such and such a time and such and such a prayer at such and such a time. And al the time of the prayer one of you should pronounce the Adhan and the oldest of you should lead the prayer."