When atheists say that belief in god is irrational, they are making an irrational statement.
Between 2300 and 3500 years ago, human beings developed the notion that god is the prime mover or the ultimate creator of the universe. To this day, this notion of god continues to motivate the theistic mind. But if god is the ultimate creator, then he is the creator of all the laws of the universe—this means that whatever god does is rational; he can, if he desires, rewrite all the laws of science and mathematics and these new laws would automatically become the new rational and the structure of the universe would transform so that everything accords with the new laws.
If god is the fountainhead of rationality, then how can the belief in god be irrational? The notion that a belief in god is irrational makes no sense.