The Forgiver - 40:12
Because when Allah ALONE was called, you disbelieved. You used to believe only when partners were associated with Him. The judgment belongs to Allah, the Exalted and the Great.
You used to believe when partners were associated with Allah:
Prophet Joseph/12:103
The majority of the people will not believe, however much you may wish.
Prophet Joseph/12:104
Yet you do not ask from them any wage. This is only a warning to the people.
Prophet Joseph/12:105
How many signs are there in the heavens and the earth that they pass by carelessly.
Prophet Joseph/12:106
And most of them do not believe in Allah without associating partners.