Salim bin Abdullah narrates from his father (Sayyiduna Abdullah bin Umar, may Allah be pleased with him). The Prophet Muhammad (peace be upon him) was performing a prayer. During it, he experienced doubt. When he finished the prayer, he said to my father, "Were you with us (in the prayer)?" He replied, "Yes." The Prophet Muhammad (peace be upon him) said, "Then why did you not prompt me?"