It is narrated from Sayyiduna Ibn al-Simmah (may Allah be pleased with him) that he said: I passed by the Messenger of Allah (peace and blessings be upon him) while he (peace and blessings be upon him) was urinating. I greeted him (peace and blessings be upon him), but he did not return my greeting. Then he stood facing a wall and scratched it with a stick that he had with him, then placed his hands on the wall and wiped his face and forearms, then returned the greeting.
(b) This narration is a supporting witness (shahid) for the narration of Abu Salih, the scribe of al-Layth, except that it is munqati' (its chain is broken): Abd al-Rahman bin Hurmuz al-A'raj did not hear it from Ibn al-Simmah; he heard it only from Umayr, the freed slave of Ibn Abbas, from Ibn al-Simmah.
(c) The hadith scholars differ about the 'adalah (reliability) of both Ibrahim bin Muhammad bin Abi Yahya al-Aslami and Abu al-Huwayrith Abd al-Rahman bin Mu'awiyah, except that their narration mentioning the forearms has a supporting witness in the hadith of Sayyiduna Ibn Umar (may Allah be pleased with them both).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 992