Compulsory Method Of Ablution
Yes it is enough. But to do the recommended way will be rewarded more. It is not a matter of sin but a matter of gaining more rewards and following best example of Prophet (PBUH). Reason mouth or neck or any other extra part is included by Prophet (PBUH) is that when he ‘washed the face’ , he would wash his mouth and nose to ensure his face is properly washed, similarly he would wash the ears and neck to ensure that the head part is properly washed. He would wash between the toes to ensure the feet were properly washed, he would repeat each step three or more times to ensure everything was washed. So the more properly you wash the part in each step, the more reward you will get. But if the minimum method described in Quran is followed, the ablution will be complete and there will be no sin.