Consequence of deliberately omitting 'Bismillah' during ablution while aware?
Chapter on Siwak and the Sunnah of Wudu
Al-Mughni
Book of Purification
Primary text
If the Basmalah is deliberately omitted during purification, the purification is invalid because an obligatory component of purification was neglected, akin to omitting the intention (*niyyah*). If it is omitted due to forgetfulness (*sahw*), the purification remains valid. Ahmad stated that he hopes there is no issue if one forgets it. Accordingly, if one remembers during the process of purification, one should utter it at that point, as forgiveness is granted for forgetfulness concerning the entirety of wudu, so it applies to a part thereof. If one deliberately omits it and then washes a limb, that washing is not counted because God's name was not mentioned upon it intentionally.
Supporting text
The opinion of Shaykh Abu al-Faraj is that uttering the Basmalah during any part of the wudu suffices in all circumstances because God's name has been mentioned upon the ablution. Some companions argue that it is not waived by forgetfulness due to the general nature of the Hadith and by analogy with other obligatory elements. The former view is preferred based on the Hadith granting forgiveness for error and forgetfulness, and because wudu is an act of worship composed of distinct actions, some of its obligations can be waived by forgetfulness, unlike other obligatory elements of general purification whose obligation is strongly confirmed.