Is it obligatory to repeat Istinja (cleansing after defecation or urination) and purify the garment with water every time a spot resembling impurity is found after performing Istinja, Wudu (ablution), and prayer, or is it sufficient to purify the garment only without repeating Istinja?

If you are certain that something has exited the posterior, then it is obligatory to perform istinja (definition)' (ritual cleansing) and purify the garment for prayer. There is no harm in delaying the purification until the time of prayer, as avoiding impurities is a condition for the validity of prayer. However, if you are not certain of its exit, then the ruling we adopt is to prioritize the original state, which is purity. This original state is not removed except by certainty. We warn against obsessive thoughts (waswas) in this matter.