Sayyiduna Ka'b bin Malik (may Allah be pleased with him) narrates that Amir bin Malik, who was called Mula'ib al-Asinnah, came to the Prophet (peace and blessings be upon him) at Tabuk. The Prophet (peace and blessings be upon him) presented Islam to him, but he refused, and he offered a gift to the Prophet (peace and blessings be upon him). The Prophet (peace and blessings be upon him) said: "We do not accept the gift of an idolater." Then he (Amir) said: Send whomever you wish to the people of Najd; I am their protector (guarantor of safety). So the Prophet (peace and blessings be upon him) sent a group, among whom was Mundhir bin Amr (may Allah be pleased with him), who was called "A'naqa li-yamut" (he hastened to die). Then Amir bin al-Tufayl heard of them. Then the narrator went on to mention the whole hadith.
Hadith Referenceالمعجم الكبير للطبراني / باب الكاف / 16212