First thing is that you can't obviously just say : You give the other one 1000€ so I want the same, maybe you both are doing the same thing, but his skills when negotiating the salary is far better than you. In lots of situations, negociation skills can make difference between people because work is not 100% about what you can do, there's also the soft skills part, including communication, management, leadership, dealing with urgent situations ...
IF I WERE IN YOUR SHOES, and I confirm that this is only my opinion, I would wait between 6 to 12 months before asking for a raise, during that time I would've built some solid arguments to negociate the raise : e.g : I've been working hard during the past months and I was able to perform 20%, or don't know how much, that's why I think ...
The other thing I want to tell is to work on your soft skills, communication is important, words are important, knowing how to talk is important. Sometimes other people are getting offers not because they're technical skills are better but it's just because they knew how to convince the interviewers that they're the best candidates for the position.
Good luck.