Is it permissible to take secular academic books for study during I'tikaf, or is I'tikaf restricted to reading the Quran and religious sciences only?

Some scholars disliked the idea of the mu'takif (one observing i'tikaf) engaging in scholarly pursuits, arguing that the purpose of i'tikaf is the purification of the heart and the discipline of the soul. They deemed it undesirable for the mu'takif to teach the Qur'an, instruct in knowledge, engage in debates with jurists, attend their sittings, or write down hadith, because the Prophet (peace be upon him) observed i'tikaf, and no reports indicate that he engaged in anything other than specific acts of worship during that time.

The Shafi'is, however, held the view that it is preferable for the mu'takif to engage in acts of obedience such as prayer, glorification (tasbih), remembrance (dhikr), and recitation (of Qur'an), as well as to engage in learning and teaching knowledge, studying, writing, and similar activities. They saw no disfavor in any of these.

In summary, engaging in these scholarly pursuits during i'tikaf does not invalidate it. The disagreement lies only in whether it is permissible for the mu'takif to engage in such activities, with the disagreement pertaining to their permissibility in terms of disfavor (karahah), not outright prohibition (hurmah) or invalidation (fasad).