From Sahih Muslim (Hadith 1535):
Malik b. Huwairith reported:We came to the Messenger of Allah (ﷺ) and we were all young men of nearly equal age. We stayed with him (the Holy Prophet) for twenty nights, and as the Messenger of Allah (ﷺ) was extremely kind and tender of heart, he therefore, thought that we were eager (to see) our family (we felt homesick). So he asked us about the members of the family that we had left behind and when we informed him, he said: Go back to your family, stay with them, and teach them (beliefs and practices of Islam) and exhort them to good, and when the time for prayer comes, one amongst you should announce Adhan and then the oldest among you should lead the prayer
Reference: Muslim 1535