What is the ruling on the prayer of one from whom drops of urine fall onto the prayer rug and the towel after showering, and it is sometimes difficult for him to wash them, and does he sin by not informing others when they use the towel?

Among the conditions for the validity of prayer is the purity of the place where the worshipper's prostration points touch. So, if the impurity is directly on the place where you pray, your prayer is not valid. However, if it is on the edge of the prayer rug and not directly on the place where you pray, then your prayer is valid. If you ascertain the presence of impurity on the towel, you should advise anyone who intends to use it, out of sincerity. Some jurists have even deemed it obligatory to inform, and sin is incurred by not doing so.