“Abdullah ibn As’ad” says:

" انْتَهَيْتُ لَيْلَةَ أُسْرِيَ بِي إِلَي السِّدْرَةِ الْمُنْتَهَي، فَأُوحِيَ إِلَيَّ فِي عَلِيٍّ بِثَلاثٍ: أَنَّهُ إِمَامُ الْمُتَّقِينَ، وَسَيِّدُ الْمُسْلِمِينَ، وَقَائِدُ الْغُرِّ الْمُحَجَّلِينَ إِلَي جَنَّاتِ النَّعِيمِ " 

Messenger of Allah [PBUH] said: in the night that I was taken to “Mi’raj”, three things about hadrat “Ali ibn abi Talib” were revealed to me: he’s “Ali” [a.s] the leader of pious ones, master of Muslims and leader of people who are going to gardens of bless.

Knowing Sahaba – vol. 3, p 587