وَعَنْ أَبِي سَعِيدٍ
قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِذَا بُويِعَ لِخَلِيفَتَيْنِ فاقتُلوا الآخِرَ منهُما»
Abu Said al-Khudri reported God’s Messenger as saying, “When allegiance is sworn to two caliphs kill the second of them.* Muslim transmitted it. * Some interpret ‘kill’ here as meaning to fight with. The tradition is directed against the possibility of two Caliphs holding power at the same time, even though the areas might be quite distinct.”
Mishkat al-Masabih 3521, Book 19, The Offices of Commander and Qadi, Hadith 16. 1 min read