Abu al-Ayyash (may Allah have mercy on him) said that he asked Sayyiduna Mu'adh bin Jabal (may Allah be pleased with him) what makes the ritual bath obligatory, and whether he could eat with his wife while she was menstruating. He said: You have asked me about what I asked the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) said: "The ritual bath is obligatory due to janabah (major ritual impurity)."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17331