Aishah (may Allah be pleased with her) narrates a similar hadith from the Prophet (peace and blessings be upon him).
This hadith was narrated by Muzahir bin Aslam alone, and he is an unknown (majhul) man, known only through this hadith. What is authentic from al-Qasim bin Muhammad is that he was asked about the waiting period of a slave woman and said: People say two menstrual cycles.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العدد / 15457