What is the authentic dhikr for wudu'?

Question:
Some people mention a hadith regarding wudu' when washing the hands?

Answer:
No, it has no basis, except after the wudu'. One mentions the name of Allah at the beginning of the wudu' and testifies to the oneness of Allah at its end; this is what is established.
Q: Is the basmalah obligatory during wudu'?
The Shaykh: It is well known that mentioning the name of Allah is recommended (mustahabb). Some scholars say it is obligatory. Ahmad (may Allah have mercy on him) and the majority of the scholars hold that it is recommended, while the second opinion is that it is obligatory. However, the hadith is weak. The hadith: The Hafiz (may Allah have mercy on him) said: ... Taken together, they rise to the level of hasan (good). In any case, the believer should not leave it out, thereby avoiding the disagreement. He should pay attention to it at the beginning of the wudu' if he remembers it. As for if he forgets or is unaware, he owes nothing.
Q: Does he say it during the wudu' if he forgot it?
The Shaykh: If he forgot it, he says it during the wudu'. And if he forgot it, it is dropped from him.