Is one who seeks a legal concession for an act that gratifies his desires, and is convinced by the saying of a reputable scholar who has his proofs, even though he is aware of the refutations of this saying, sinful?

There are two types of dispensations (rukhṣa): legitimate, Sharia-prescribed dispensations established by the Quran and Sunnah, such as shortening prayers (qaṣr) and combining them (jamʿ) during travel. It is recommended to avail oneself of these, and it may even be obligatory. The second type comprises dispensations from the jurisprudential schools (madhāhib), which are a scholar's fatwa permitting something in a matter of scholarly disagreement. Following these dispensations without a legitimate legal preference or without imitating someone one believes to be the most knowledgeable, but merely out of desire and following whims, is reprehensible and impermissible. However, there is no objection to availing oneself of dispensations and combining rulings from different schools of thought through ijtihad (independent reasoning) and tarjih (weighing evidence), or for a layperson to imitate someone they believe to be the most knowledgeable. Similarly, there is no harm for someone who takes some dispensations due to need or hardship, or when a ruling is unclear to them and no single opinion prevails due to the strength and equal weight of the evidence, or for a layperson if they ask scholars who differ in their fatwas and none of them is considered more trustworthy than another.