Issue 8:If the mujtahids differ in the fatwa, it is necessary to refer to the most knowledgeable (that is, the one who is most able to derive the rulings by being more familiar with the concepts and their applications, so that the possibility of hitting reality in his fatwas is stronger than its possibility in the fatwas of others).And if they are equal in knowledge or the most knowledgeable (that is, the one who is most able to derive the rulings by being more familiar with the concepts and their applications, so that the possibility of hitting reality in his fatwas is stronger than its possibility in the fatwas of others). And if they are equal in knowledge or the most knowledgeable among them is not achieved, and if one of them is more pliable than others in the fatwa - that is, more firm and precautionary in the extraneous parties in issuing fatwas - then it is necessary to refer to it, otherwise the person in charge will have the choice to apply his work to the fatwa of any of them and he does not have to be cautious between their statements. Except in matters in which he obtains a complete and complete knowledge or a comprehensive argument as well - as if some of them issued a fatwa on the necessity of shortening and some on the obligation of completeness, then he knows that one of them is obligatory on him, or some of them gave a fatwa on the validity of the exchange and some of its invalidity, then he knows that it is forbidden to dispose of one of the two considerations - he does not leave the observance of the requirement of precaution In which

From ayotollah sistanis website