Question: Has Islam commended that while beginning a particular work if someone sneezes the work has to be postponed?
Answer: There is no such command in Islam and basically the spirit of Islam does not agree with such superstitions. Rather it commands that if you are going to begin some work and someone is doing divination against it, you must not pay attention to that person, you must rely on Allah and begin your work. Islam has even considered divination a sign of polytheism.
Although it is commanded with regard to the sneeze that if one of you sneezed one should utter Alhamdo lillaah (Praise be to Allah) and the others should say Yarahamokumllaah (May Allah have mercy on you). The person will then respond with the prayer: Yaghfirullaaha lakum (Allah shall forgive you).
However, to refrain from doing something or to delay for even a little, or to discriminate between one or two sneezes are all baseless things. Therefore a true Muslim should avoid such useless superstitions.