Some Hadiths on the Matter
In his masterful collection of Prophetic hadiths, Riyadh al-Salihin [Gardens of the Righteous], Imam Nawawi placed an entire chapter called “The Prohibition of Going to Soothsayers, Astrologers and Diviners, and of Seeking Omens.”
Some of the hadiths in that chapter are as follows, all of which clearly indicate the immense gravity and seriousness of the sin:
“If one goes to a soothsayer, asks about something, and believes it, his prayer will not be accepted for forty days.” [Muslim]
“Divination and taking omens from the flight of birds are types of idolatry.” [Abu Dawud]
“If one takes knowledge from the stars [i.e., astrology], he in fact takes a branch of sorcery. The more knowledge he gains [of that], the more sin he gains.” [Abu Dawud; commentary from Munawi, Fayd al-Qadir]
And Allah alone gives success.