Sayyiduna Malik bin al-Huwayrith (may Allah be pleased with him) says: We came to the Messenger of Allah (peace and blessings be upon him) as young men of similar age, and we stayed with him (peace and blessings be upon him) for twenty nights. The Prophet (peace and blessings be upon him) was very merciful and gentle-hearted. When he (peace and blessings be upon him) sensed that we were longing to go to our families, he asked us about those we had left behind, and we told him. He (peace and blessings be upon him) said: "Return to your families and stay among them, teach them and command them." And he (peace and blessings be upon him) mentioned some things, some of which I remembered and some of which I forgot. And he (peace and blessings be upon him) said: "'Sallu kama ra'aytumuni usalli' (Pray as you have seen me pray). When the time of prayer comes, one of you should give the adhan, and the eldest of you should lead the congregation."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5293