Sunan Ibn Majah, Book 1, Hadith 142 (In-Book) ⓘ
It was narrated that 'Ali said: "The Messenger of Allah said: 'If I were to appoint anyone as my successor without consulting anyone, I would have appointed Ibn Umm 'Abd.'"
حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا وَكِيعٌ، حَدَّثَنَا سُفْيَانُ، عَنْ أَبِي إِسْحَاقَ، عَنِ الْحَارِثِ، عَنْ عَلِيٍّ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ " لَوْ كُنْتُ مُسْتَخْلِفًا أَحَدًا عَنْ غَيْرِ مَشُورَةٍ لاَسْتَخْلَفْتُ ابْنَ أُمِّ عَبْدٍ " .
also referenced under: Hadith 137 (Reference) & Volume 1, Book 1, Hadith 137 (DarusSalam)