“Abraham responded and said: Behold now, I have presumed to speak to my Lord, and I am dust and ashes” (Genesis 18:27). “Behold now, I have presumed […and I am dust and ashes]” – he said: ‘Had Amrafel killed me, would I not be dust now? Had Nimrod burned me, would I not be ashes now?’ The Holy One blessed be He said to him: ‘By your life, you said: “I am dust and ashes,” by your life, I will provide atonement to your descendants through them,’ as it is stated: “They shall take for the impure from the dust of the burning of the purification” (Numbers 19:17), “a pure man shall gather the ashes of the heifer” (Numbers 19:9).
We learned: What is the procedure for fast days? They take out the ark to the city square and place burnt ashes upon the ark.62Mishna Taanit 2:1. After this, all those gathered in the square would place ashes on their heads (Mishna Taanit 2:1). Rabbi Yudan bar Menashe and Rabbi Shmuel bar Naḥman, one of them said: ‘[This was to recall] the merit of Abraham,’ and one said: ‘The merit of Isaac.’63The ashes, as it were, of his being sacrificed on Mount Moriah.
According to the one who says the merit of Abraham, [he said:] “I am dust and ashes.”64So that either dust or ashes may be used in this ritual. According to the one who says the merit of Isaac: Ashes only. The statement of Rabbi Yudan is in disagreement with this.65With the latter opinion, that only ashes may be used. As Rabbi Yehuda ben Pazi66Earlier called Rabbi Yudan, for short. would proclaim in public and say: ‘Anyone to whom the public attendant did not come to place ashes on his head, let him take dirt67Translation follows emendation of Yefe Toar. and place it on his head.’ The statement of Rabbi Yehuda ben Pazi shows that dust is the same as ashes.