Musnad Abu Ya'la al-Mawsili 152:175

Yahya narrated to us, from Sufyan, my father narrated to me, from Abu Ya'la, from al-Rabi' ibn Khuthaym, from Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) drew a square line for us, and he drew lines in its middle, like this, to the side of the line, and he drew a line outside it. Then he said: "Do you know what this is?" We said: "Allah and His Messenger know best." He said: "This is the human being," referring to the line in the middle of the square, "and this is the appointed term (ajal), and these are the accidents (al-a'rad) for the lines that bite him. If he misses this, this strikes him. And that is hope (al-amal)," referring to the line outside.