The eminent Muslim scholar and renowned Da`iyah, Sheikh `Abdel Khaliq Hasan Ash-Shareef, states: “Washing the neck is not a pillar or a prerequisite of wudu’. However, if one used to wash it while performing wudu’ without believing or thinking that it is a sunnah or prerequisite of wudu’ there is nothing wrong with that. However, if one used to wash the neck believing that it is a sunnah or a perquisite for the validity of wudu’, then this is not permissible.”