Is reading a book on the science of body language that includes a section on soothsayers and diviners, without believing what is stated therein from the sayings of the soothsayers, considered going to them? And does that entail the non-acceptance of prayer for forty days?

It is forbidden to read books that encourage being deluded by soothsayers, especially if truth is mixed with falsehood within them. What is called "body language" relies on firasa (perspicacity or intuitive insight), which is the ability to know some inner states through outward signs. This firasa may be an inherent disposition possessed by both believers and disbelievers. Authors' claims regarding the accuracy of their studies must be verified, as they may be general matters common to most people. If a soothsayer discovers people's conditions, it could be due to their sharp intelligence or their dealings with jinn. The phrase "The astrologers have lied, even if they spoke the truth" is correct in meaning and is confirmed by Prophetic narrations that describe soothsayers as "nothing" and that their occasional truthfulness comes from jinn snatching a word of truth and mixing it with a hundred lies. Reading stories about diviners with the intention of learning is forbidden, even if it does not fall under the threat of "Whoever comes to a diviner and asks him" if the questioner does not intend to act upon what they say, yet it may lead to temptation. It is disliked to read anything containing astrology or horoscopes, as it is a type of soothsaying, and whoever believes in it has committed disbelief. What is clearly forbidden, such as teaching magic and soothsaying, must be destroyed, and what is doubtful must be avoided.