(And) if you differ in anything amongst yourselves, refer it to Allaah and His Messenger, if you believe in Allaah and in the Last Day. That is better and more suitable for final determination[al-Nisa 4:59]

There is no scholar who does not have some issues in which he strove to make a decision on the basis of ijtihaad but failed to reach the right answer, but he is excused for that and he will have a reward for his ijtihaad, as the Prophet (peace and blessings of Allaah be upon him): If a judge passes a ruling to the best of his ability and knowledge and gets it right, he will have two rewards. If he passes a ruling to the best of his ability and knowledge but gets it wrong, he will have one reward. (al-Bukhaari, 7352; Muslim, 1716)