A Message To Every Youth
In his book al-Fawaid, he said (Ibn al-Qayyim):
There are ten useless matters that cannot be benefited from:
Knowledge that is not implemented
An action that is empty of sincerity, and is not based on the correct example
Wealth that is hoarded, as the owner neither enjoys it during this life, nor obtains any reward for it in the Hereafter
The heart that is empty of love and longing for Allāh, and of seeking closeness to Him
A body that does not obey and serve Allāh
Loving Allāh without seeking His pleasure
Time that is not spent in expiating sins or seizing opportunities to perform deeds of righteousness that will bring one closer to Allāh
A mind that thinks about issues which bring about no benefit
Serving those who neither bring you close to Allāh or benefit you in your life
Hoping and fearing one who is under the authority of Allāh, and whose forehead is in His Hand, while he cannot bring any benefit, harm, life, death, or resurrection to himself.
However, the greatest of these matters is the wasting of the heart, and the wasting of time. Wasting the heart is done by preferring this worldly life over the Hereafter, and wasting time is done by having incessant hopes. All evil is in following ones desires and having incessant hopes, while all goodness is found in following the right path and preparing oneself to meet Allāh, and Allāh is the source of Assistance.
Here, he summarized all evil in these two issues: wasting of the heart, and wasting of time. Wasting the heart is done by preferring this worldly life over the Hereafter, and wasting time is done by having incessant hopes, and incessant hopes and the following of ones desires are the ultimate manifestation of evil.