It is narrated from Sayyiduna Malik bin al-Huwayrith (may Allah be pleased with him): I came to the Prophet (peace and blessings be upon him) with a group of my people, and we stayed with him (peace and blessings be upon him) for twenty days. He was very merciful and gentle. When he (peace and blessings be upon him) saw our longing for our families, he said: "Go back and stay among them, teach them and pray. When the time of prayer comes, let one of you give the adhan, and let the eldest of you lead you in prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 1806