Four Enemies
Shaykh Ahmad Ibn Amīr—may Allāh bless his soul—said:
You have four enemies:
1. Shaytan: and his weapons are a full belly, and his prison is hunger.
2. Desire: and its weapon is speech, and it is imprisoned by silence.
3. This world: whose weapon is to meet people, and it is imprisoned by retreat.
4. The self: whose weapon is sleep and it is imprisoned by sleeplessness.
Shaykh Ahmad Ibn ‘Isā az-Zarrūq—may Allāh bless his soul—commented:
“One is required to take the middle path in these four matters, and to begin with the most important. Whoever finds that hunger is more important to him, he should not eat more than he needs, and to whomever silence is more important, he should not speak except about what concerns him. Whoever finds that retreat is more important to him should not meet people, but should keep away from them. Whoever finds that sleeplessness is more valuable to him, should sleep only the amount he needs. Excess is harmful in everything. Too much hunger can spoil reflection. Too much silence can spoil wisdom. Too much sleeplessness leads to insanity, and too much retreat leads to boredom.”

No Rest
Shaykh Abū al-Abbās al-Mursī—may Allāh bless his soul—said:
Those who know God do not rest tranquilly in God, for to rest tranquilly in God is a sign that one considers oneself safe; however, no one considers himself safe from God’s scheming but those who are spiritually lost.

Insight
Shaykh Abū al-Hasan ash-Shādhilī—may Allāh be pleased with him—said:
My heart was enlightened one day and I saw the kingdom of the seven heavens and the seven earths. I then committed a minor sin, after which the vision was concealed from me. I was astonished that such a trifling occurence could conceal from me something so momentous. Just then someone said to me, ‘[Spiritual] insight is like [physical] sight: The tiniest thing that gets in the eye can obstruct one’s vision.’

Doubts
Shaykh Ibn Atā’allāh al-Iskandarī—may Allāh bless his soul—said:
Shaykh Abū al-Abbās al-Mursī—may Allāh be pleased with him—had a profound dislike for obsessive doubts concerning one’s ritual purity and the validity of one’s canonical prayers, and he found it burdensome to be with people who were prone to such preoccupations. One day when I was with him, someone said to him, “Master, so-and-so is a man of knowledge and integrity but he’s prone to obsessive doubts.”
“Where is his knowledge and integrity, then?” the Shaykh asked. “[True] knowledge is imprinted on the heart as whiteness [inheres] in that which is white and as blackness [inheres] in that which is black.”