It is narrated from Sa'id bin Umayr; he said: I sat with Sayyiduna Abdullah bin Umar and Sayyiduna Abu Sa'id (al-Khudri) (may Allah be pleased with them), and one of them said to the other: I heard the Prophet (peace and blessings be upon him) mention how far the sweat of a human being will reach, and he (peace and blessings be upon him) said: "(It will reach) to the lobes of his ears." And the other said: "The sweat will bridle him." And Sayyiduna Ibn Umar (may Allah be pleased with them both) gestured and drew a line from the lobe of his ear with his index finger (that is, he made it clear by marking it). The chain of this hadith is sahih (authentic), but the two Shaykhs (Bukhari and Muslim) did not record it.