(470) بَابُ التَّسْلِيمِ عَلَى الأَمِيرِ
Tamim ibn Hadhlam said, "I will mention the first to be greetedas 'Amir' in Kufa. Al-Mughira ibn Shu'ba left by the Bab ar-Rahba and aman of Kinda came up to him. They claim that it was Abu Qurra al-Kindi.He greeted him and said, 'Peace be upon you, O Amir, and the mercy of Allah.'He disliked it. So the man said, 'Peace be upon you, O Amir, and the mercyof Allah. Peace be upon you. Am I one of you or not?'" Sammak ibn Salamaad-Dabi said, "After that it became an established practice."
Reference: Al-Adab Al-Mufrad 1026
In-book reference: Book 42, Hadith 63
English translation: Book 42, Hadith 1026