Malik stays busy all day running a business to support his family. His aging parents have moved in with him, and he struggles to provide for their care. Malik has a teenage son who has recently left school without his approval. When Malik begins to feel overwhelmed by these obstacles, he repeats the statement, “There is no God but Allah and Muhammad is the messenger of Allah.” Just this act calms him because he feels that he is fulfilling a pillar of Islam. What pillar is Malik practicing?