It is narrated from Sayyiduna Khalid bin Sa'id (may Allah be pleased with him); he said: The Prophet (peace and blessings be upon him) sent me to Yemen and said: "Whichever tribe of the Arabs you pass by and hear the call to prayer (adhan) among them, do not trouble them; and those among whom you do not hear the adhan, invite them to Islam, and if they do not accept, then fight them (in jihad)."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 4101