A generalized method due to Noor and Waseem is studied for solving nonlinear equations in Banach space. The Noor-Waseem method is of order three. But, the convergence of this method was shown assuming that the fourth derivative, not on the method, exists. This constraint is limiting its applicability. Moreover, neither computable error bounds nor results about the uniqueness of the solution were given. We address all these problems using only the first derivative which only appears on the method. Hence, we extend the applicability of the method under consideration. Our techniques can be used to obtain the convergence of other similar higher order methods using assumptions only on the first derivative of the operator involved.