3 JB Company engaged in garment business found itself in an unstable condition due to Covid 19. It's incorporators . The creditors Mr. Reyes and Mr. Bautista with 100 other stockholders agreed to take over the business and accept stocks as payment for what the corporation owed them. After this was done, they became two largest stockholders in the corporation RNB Inc . They also entered into an agreement where the agreed not to sell, transfer or dispose of their present stocks in RNB. What is the source of the obligation not to sell? Explain.