Musnad Ahmad 956:3

Muhammad ibn Ja'far narrated to us, Sa'id narrated to us, from Muhammad ibn al-Munkadir, from a man, from 'Abdullah ibn Hanzalah ibn al-Rahib: That a man greeted the Prophet, may Allah bless him and grant him peace, while he had urinated, so the Prophet, may Allah bless him and grant him peace, did not return the greeting to him until he gestured with his hand toward the wall—meaning that he performed tayammum.