The Mother of the Believers, Sayyidah Umm Salamah (may Allah be pleased with her), narrates: "When the Messenger of Allah (peace and blessings be upon him) was in a state of major ritual impurity (janabah), he would not eat anything until he had performed ablution like the ablution for prayer."
Hadith Referenceالمعجم الأوسط / باب الجيم / 3368
Hadith Takhrij«أخرجه أحمد فى «مسنده» برقم: 27195، والطبراني فى «الكبير» برقم: 707، 980، والطبراني فى «الصغير» برقم: 325»