Imam Ali (a.s) was asked how did he come to know Allah, whereupon he (a.s) replied: "I knew Allah by peeling away determination and obliterating want. I wanted, so a barrier formed between myself and what I wanted. I was determined but the judgement overturned my determination. So I knew that Al-Mudabber (the one who decrees) is other than me."
Tawhid Al-Sadoq, Ch.41, H.6