Taqwâ (piety) has three levels:
1. Do not use such things or wealth that the jurists and ulamâ have declared harâm (forbidden), as using these will result in one becoming a fâsiq (open rebellious sinner), and his testimony will be rejected in court. This is the level of piety of the common Muslim.
2. The second level of piety is that of the sulahâ (pious). This means that one should abstain from doubtful things, even though the Muftis, based on outwards circumstances, have declared them to be halâl. However, these items are such, that there is a possibility of hurmat (prohibition, thus they become doubtful. The sulahâ abstain from such type of food.
Rasulullâh Sallallahu Allaihi Wasallam said, “Leave that in which there is doubt, for that in which you do not have doubt.” Ibn Hibbân(722), Tirmidhi (2518), Hâkim (2/13)
3. The third level is that of the atqiyâ (those having taqwâ/abstinent). Rasulullâh Sallallahu Allaihi Wasallam said, “A person cannot reach the rank of the muttaqin (those having taqwâ), until he does not leave out the harmless things, for fear of getting engaged in those things in which there is harm.” Tirmidhi (2451), Hâkim (4/319), Ibn Mâjah (4215)
Umar Radhiallahu Anhu used to say, “We used to leave out nine-tenths of halâl, out of fear of falling into harâm.” Musannaf of Abdur Razâq (8/152)
Based on this principle, some of Allâh Ta’aala’s pious servants would only suffice on 99 dirhams when they were eligible to receive 100. When they had to fulfil anyone’s right, they would give extra. When claiming their right, they would take less!
Umar bin Abdul Aziz Rahmatullahi Allahi would cover his nose, when musk was weighed in his presence in the Baitul-Mâl (public treasury).
When asked regarding this, he remarked, “The benefit of it is in its fragrance.” Abu Nua’ym in Hilyah, Bayhaqî in Az-Zuhdul Kabîr (919), Taârikhe Dimishq (28/64)
This is the reason for abstaining from delicious halâl food, and permissible forms of beautification. There is fear that once habituated to it, one’s nafs will overpower a person, and thereafter lead him to prohibited desires. The prohibition of the Qurân of longingly gazing at the abundance of wealth and material chattels of the disbelievers, and towards their status and honour, is because the beauty and lustre of one’s îmân diminishes, due to this outward glamour. When the love and desire of worldly wealth and goods overtakes one, the love of îmân does not remain in the heart. A pious person once said, “He whose clothing is thin, his Dîn is also thin.” In short, according to the abstinent, only that wealth which is halâl, is presently devoid of any form of doubt, and devoid of any possibility of causing harm in future, is worthy of consumption.
Tabligh-al-Deen – The forty foundations of the Religion by Imam Abu Hamid Muhammad ibn Muhammad al-Ghazaali Rahmatullahi Allaihi. Pg 32-33.