Adverting Excessive Thinking
Know that thinking is needed to remember what was forgotten, and to think about future benefits. However if thinking is about that which is not fruitful it will be harmful, and if it is excessive it will exhaust the body.
The hypocrites say, “Scholars should leave thinking for sometime, lest they exhaust their bodies.” I said, a wise person should not stop thinking about what he can attain.
However when a layman thinks of becoming the Caliph, that he is as knowledgeable as Abu Hanifah or Al-Shafi’i, that he is an ascetic exactly like Bishr al-Hafi and Mar’uf al-Karhi, to have the wealth of ‘Abdul Rahman ibn ‘Awf, these thoughts exhaust the body, especially if he is only thinking and is idle (instead of working hard to achieve what he wants).
A person should rather think about that which is possible for him to achieve, and what he can attain from good deeds. He should also think about his struggle against evil. For many sinners reflected on their consequences and repented, many kings reflected on the vanity of this life, to became ascetic.
Ibn ‘Abbas (radiyAllahu ‘anhuma) said, “Praying two rak’at with contemplation is better than praying all night while the heart is heedless.” (1)
Umm al-Darda’ (radiyAllahu ‘anha) was asked, “What was the best deed of Abu’l-Darda?” She said, “Contemplation and thoughtfulness.” (2)
Malik ibn Dinar stood on his feet praying until dawn and said,”The people of hellfire, in their chains and iron collars, kept presenting to me until dawn.”
Some wise men used to say, “Warding off thinking brings blindness.”
 Reported by Ibn ul-Mubarak in the Book of Zuhd p.403, and Muhammad ibn Nasr in the Book of Qiyam-ul-Layl p.60.
 Reported by Ibn ul-Mubarak in the Book of Zuhd p.302 thought the chain of ‘Awn ibn ‘Abdullah from Umm al-Darda’ that he was asked, “What was the most frequent act of Abu al-Darda?” She said, “Contemplation.” Reported by Abu Nu’aym in al-Hilyah [1:208] “ She said, “Contemplation and thoughtfulness” [1:209] Abu l-Darda said, “Contemplation for an hour is better than praying one whole night.”
From the Book: “Disciplining the Soul” Ibn al-Jawzi (d.597H)