It is narrated from al-Sharid al-Thaqafi (may Allah be pleased with him) that Umar bin al-Khattab (may Allah be pleased with him) led the people in prayer while in a state of major ritual impurity (janabah). He (may Allah be pleased with him) repeated the prayer himself, but he did not order those who had prayed behind him to repeat it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4073