You need the consent or agreement of a majority of the owners. That is majority by ownership interest, so if it was owned equally by the three of you (1/3 each), for example, two of you together have a majority (2/3) and can make the decision to sell. The exception to this would be if the articles of incorporation, operating agreement, or other document(s) creating or governing the business specifically require unimous consent for this; if so, you have to do what the three of you previously agreed.