What is the ruling on the prayer of one who has an opening before the anus from which stool exits, leading to the defilement of his clothes?

Prayer is not valid without purification from both major and minor ritual impurity and from defilement. Therefore, one must take precautions and wear undergarments that are removed before prayer, then purify oneself and perform the prayer. If it is not possible to pray with the congregation, there is no harm in praying alone with complete purity, because purity is a condition for the validity of prayer and takes precedence over the virtue of congregational prayer.