The Messenger of Allah (s.a.w.a.) said that on the night of Meraaj, when he (s.a.w.a.) passed the gates of light, Allah talked to him (s.a.w.a.) and said: O Mohammad! Convey My Salaam to Ali b. Abi Talib (a.s.), and inform him that he is My decisive proof on all creatures after you. I pour the rain of My blessings on My slaves through him; I keep everything evil away from them through him; and he is My decisive proof on them when they meet Me.
So they should follow his commands, obey his orders, and abstain when he abstains. If they do so, I will seat them next to Me and I will allow them to enter My Paradise. If they do not, I will put them with the worst of My enemies in Hell and I will not care. Bashaarah al-Mustafa Le Shiah al-Murtaza p 157 Behaar al-Anwaar v 38 p 138