Allaah the Exalted said [to Shaytaan]:

Then get out from here, for verily you are accursed, rejected. And verily, upon you is the curse till the Day of Judgement. He said: O my Lord grant me respite till the Day they are raised up. He (Allaah) said: Then you are of those who have been granted respite. Till the Day of the appointed time. He (Iblees) said: Because you have put me in the wrong I will beautify for them (what is on) earth and I shall mislead them all. Except your servants among them who are sincere.

Allaah further went on to say:

Indeed you have no authority/power over My servants.

In this passage Shaytaan has made a promise, in front of Allaah, that he will misguide the whole of mankind. However, he did make an exception: The sincere servants of Allaah, and Allaah too reiterated to him, that he can have no authority over Allaah's servants, those that are sincere.