In fact, there is no proof from either the Qur’an or the authentic Prophetic Hadiths that wiping over the neck is a prescribed part of ablution or even one of the Sunnan acts of ablution.
In his book Fiqh As-Sunnah, the late Azharite scholar Sheikh Sayed Sabiq, may Allah rest his soul in peace, states that “the narrations cited in wiping over the neck are subject to controversy and they are not authentic. But, one may follow them as part of general cleanliness.”
Focusing more on the question in point, Sheikh `Abde-Khaliq Hasan Ash-Shareef, a prominent Muslim scholar and Da`yah, states the following:
“Wiping over the neck is not among the Sunnan acts of Wudu’. However, if the person feels that his neck is unclean and just wants to wipe it as a form of cleansing it while making ablution, then there is nothing wrong. However, it is not acceptable to make it a habit when performing every Wudu’ because this renders the act into an innovation or Bid`ah.
The ideal conduct of a Muslim is to follow the very steps of the Prophet, peace and blessings be upon him, while making Wudu’ and never miss anything or add any act that does not belong to it.”

Thus, it has become clear that wiping over the neck is not an obligatory part of the ablution nor is it a Sunnah act. However, if the person does it, he is not committing Bid`ah as long as he does not intend to add an act to ablution that is not of it, but rather the person wipes the neck as a part of general cleanliness, when necessity warrants doing it.