‘Asceticism’ (zuhd) is [to abstain] from what has no benefit whether due to the absence of its benefit or its being preferred over, since it is passed over for what has more benefit than it, or as a result of its harm exceeding its benefit. As for the true or preferable benefit then asceticism from it is foolishness.
‘Piety’ (wara) is to abstain from what is harmful so it involves what is prohibited and doubtful since they definitely cause harm. How he who seeks refuge from doubts seeks to exonerate his honour and religion, while he who falls into doubts, also falls into that which is prohibited. He is like the one who herds his animals around a protected area on the verge of falling into it.
With regards to piety and abstaining from that which is not harmful or which has some harm that is outweighed by its good – whether due to being coupled with achieving a prevailing benefit or warding off another prevailing harm – then it is ignorance and oppression. And that includes three areas where one should not be pious or abstain from: the ‘sufficiently’ beneficial, the ‘prevailingly’ beneficial and ‘absolutely’ beneficial. They are like those things which are categorised as absolutely ‘permissible’, ‘recommended’ or ‘obligatory’, such that piety and abstention from them is deviation.
Here I will mention some details regarding that:
Asceticism is in contrast to desire (raghba). It is said: ‘So-and-so is an ascetic regarding such-and-such,’ and ‘So-and-so is desirous regarding it’. ‘Desire’ is a type of wish and asceticism regarding something is the lack of wishing for it, whether accompanied by the presence of dislike for it or a lack of wish or dislike for it so that one is not wishful or disinclined towards it. Anyone who is not desirous regarding something and at the same time he wishes for it, he is an ascetic regarding it.
Just as asceticism is praiseworthy in the path of Allah in regards to what Allah induces one to abstain from of the comforts of the world life, thus desiring and wishing are praiseworthy when Allah holds as praiseworthy his wishes and desires. Due to this, the foundation for the path is ‘wishing’, just as Allah, exalted is He, said: “And do not drive out those who call upon their Lord morning and evening, wishing for His Face.” (al-Anam 6:52) And He, exalted is He, said: “And whoever wishes for the Afterlife and strives for it with its due effort, while he is a Believer, then these, their effort will be appreciated.” (al-Isra 17:18) There are numerous similar ayahs.
Gardens of Purification by Ibn Taymiyyah Pages 98-99