Hadith 31-313

وَبِإِسْنادِهِ عَن الحُسَيْنِ بْنِ عَلِى‏عَلَيْهِمَا السَّلاَمُ قالَ: قالَ لي‏ بُرَيدَةُ أمَرَنا رَسُولَ اللَّهِ أَن نُسَلِّمَ عَلَى أَبِيكَ بِأَمرَة المُؤْمِنِينَ.

According to the same documentation, on the authority of Al-Husayn ibn Ali (a.s.), “Burayda told me that God’s Prophet (S) ordered that they (the people) call my father the Commander of the Faithful (a.s.).”