He said: Ḥasad (envy) in the Book and the Sunnah is of two kinds: these meanings are also found in the lexicon. The first is the type of ḥasad that is not forbidden. Some of this is obligatory (farḍ), some is a virtue (faḍīla), some is permissible (mubāḥ), and some leads to deficiency and the forbidden (ḥarām).
I asked: What is the ḥasad that is not forbidden? He replied: It is munāfasa (rivalry in goodness). Upon this, I asked: What evidence is there that munāfasa is ḥasad? He replied: Allah has said: 'So let the competitors compete for that' (al-Muṭaffifīn 83:26).
Allah has described ḥasad as an act of the qalb (the heart). His describing ḥasad is because it is an act that occurs with the qalb, not with the body. The sorrow that arises from ḥasad and the abandonment of the initial state is the disliked aspect of ḥasad. Ḥasad eliminates the motivation to act from the qalb. What it removes with aversion, it also prevents the limbs from performing. If one cannot silence his shayṭān (devil), he cannot prevent his own nature from struggling (mujāhada) with itself (the one who envies is consumed inwardly). (Riʿāya, 322)
The effect of ḥasad appears in you before the emergence of the enemy (shayṭān). Al-Aṣmaʿī said: I saw a Bedouin who was one hundred and ten years old, and I asked him: What has prolonged your life? He said to me: I abandoned ḥasad, and so I remained. Ibn Mubārak said: What is in the qalb of the one who envies me...