Musannaf Ibn Abi Shaybah

Hasan (may Allah have mercy on him) was asked: If a minor girl is divorced, how will she observe her waiting period (‘iddah)? He replied: She will observe her ‘iddah according to months; if she gets her menses before the months are completed, she will start her ‘iddah again based on her menses. If she gets her menses after the months are completed, then her ‘iddah is complete.