Is it correct to say that an impediment (hâ'il) during Wudu', if it is very small, like the tip of a needle or a speck of dust, is excused based on the principle of removing hardship (raf' al-ḥaraj)? And what should one do if they doubt the presence of an impediment before or after Wudu'?

Maliki jurists differed regarding a slight barrier: is it overlooked, or is redoing (the ablution) obligatory? The established position in the Madhhab is that redoing it is obligatory, and that a barrier is not overlooked even if slight. This is the view of Ibn al-Qasim. As for those who permitted overlooking a slight barrier, their intention was after the event had occurred; however, initially, its removal is obligatory. Sheikh al-Islam preferred overlooking a slight amount of what prevents water from reaching the skin. The more cautious approach is to act upon the opinion of the majority, which states that if one leaves a spot unwashed, or if there is a barrier, even a slight one, on the limbs of ablution, then their Wudu' is not valid. If one finds a barrier after ablution and does not know whether it was there before or after the ablution, the original presumption is that it occurred after the ablution.