It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) ate the meat of a shoulder, or (he said) meat, then prayed, and he neither rinsed his mouth nor touched water.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 712