The explanation for this narration is that the "mentioning of Allah’s سبحانه وتعالى name" here refers to the intention (niyyah) which we have already stated is obligatory. As for the other verbal utterances, they are recommended (mustahabb) rather than obligatory. The evidence for this interpretation lies in the previous narration, where it was stated that if someone does not mention Allah’s سبحانه وتعالى name, only the parts of the body touched by water are purified. If mentioning Allah’s سبحانه وتعالى name were obligatory, then failure to do so would render the entire ablution invalid, and no part of the body would be considered purified at all.
Commentary #3