Is the invocation of Allah's name in ablution obligatory?

The questioner : Regarding the invocation of Allah's name, O Shaykh, is it obligatory or not?

The Shaykh : Yes, the invocation of Allah's name in ablution is not obligatory, but it is a recommended practice (sunnah). This is because there is doubt regarding the authenticity of the hadith on this matter. Imam Ahmad (may Allah have mercy on him) said that nothing is established in this chapter. Imam Ahmad is, as we all know, one of the imams of this field and one of its preservers. So, if he said that nothing is established in this chapter, then there remains some doubt in one's mind about the hadith. And if there is doubt about its authenticity, then a person is not justified in obligating the servants of Allah to do something that is not established from the Messenger of Allah (peace and blessings be upon him). Therefore, we hold that the invocation of Allah's name in ablution is a recommended practice (sunnah). However, for one in whose possession the hadith is established, it is obligatory for him to act according to its implication, namely that the invocation of Allah's name is obligatory in ablution. This is because the correct interpretation of his statement is that it is a negation of validity, not a negation of perfection. But if the hadith were established, we would say that the invocation of Allah's name is obligatory. Since it has not been established in a way that gives a person peace of mind to obligate the servants of Allah the Exalted to invoke His name in ablution.
I hold that the invocation of Allah's name is a recommended practice (sunnah) and not obligatory. This is the choice of al-Muqaffi, the author of al-Mughni (may Allah have mercy on him), that the invocation of Allah's name is a recommended practice (sunnah) and not obligatory.