Is it obligatory to wash money if it has been afflicted by a slight impurity, or is it overlooked, and what is the ruling on what has been spent from it before purifying it?

Money, like other things, falls under the ruling regarding the removal of impurity that may affect it. If it is affected by a venial impurity, such as a small amount of blood, then there is no harm in not purifying it. However, if it is affected by a non-venial impurity, then it is obligatory for anyone who wishes to pray while carrying it to purify it, because avoiding impurity is one of the conditions for the validity of prayer according to the majority of scholars. If purifying it is difficult, or if there is a fear of its monetary value being diminished, then it is permissible to adopt the view of Sheikh al-Islam Ibn Taymiyyah, which is to pardon all minor impurities absolutely. This is also the view preferred by Sheikh Al-Uthaymeen in Al-Sharh Al-Mumti’.

The more cautious approach for the one carrying it is to avoid praying while carrying it. As for the money that has been spent before being purified, there is no way to remedy the situation. One must seek forgiveness for the shortcoming in this matter, and one must also be wary of falling into waswasah (obsessive whispering) concerning the issue of impurities.