Fiqh-us-Sunnah Volume 3, Zakaat and Fasting, Fiqh 3.151.

It is preferred for the one who is making i’tikaf to perform many supererogatory acts of worship and to occupy himself with prayers, reciting the Qur’an, glorifying and praising Allah, extolling His oneness and His greatness, asking His forgiveness, sending salutations on the Prophet, upon whom be peace, and supplicating Allah – that is, all actions that bring one closer to Allah. Included among these actions is studying and reading books of tafsir and hadith, books on the lives of the Prophets, upon whom be peace, books of fiqh, and so on. It is also preferred to set up a small tent in the courtyard of the mosque as the Prophet did.

It is disliked for one to engage himself in affairs that do not concern him. At-Tirmizhi and Ibn Majah record on the authority of Abu Basrah that the Prophet said: “Part of a man’s good observance of Islam is that he leave alone that which does not concern him.” It is, however, disliked for a person to think that he can draw closer to Allah by not speaking. Al-Bukhari, Abu Dawud, and Ibn Majah record from Ibn ‘Abbas that while the Prophet was delivering a speech, he saw a man standing and asked about him. The people said: “He is Abu Israel. He has vowed to stand and not to sit, and not to speak, and to fast.” The Prophet said: “Order him to speak, go to the shade, to sit, and to complete his fast.” Abu Dawud related from ‘Ali that the Prophet said: “There is no orphan-hood after one has passed the age of maturity, and there is no non-speaking for a day until the nightfall.”