פירוש על שמות 16:1

בחמשה עשר יום ON THE FIFTEENTH DAY — The day of this encampment is specially mentioned because on that day there came to an end the cake (provisions) they had brought with them from Egypt and they now needed the Manna, thus informing us that of the remains of the dough they had prepared in Egypt (cf. Rashi on Exodus 12:33) they ate sixty-one meals. For the Manna fell for them on the sixteenth day of Iyar, which was the first day of the week, just as is stated in the Treatise Shabbat 87b.

AND THEY TOOK THEIR JOURNEY FROM ELIM, AND ALL THE CONGREGATION OF THE CHILDREN OF ISRAEL CAME UNTO THE WILDERNESS OF SIN. Scripture speaks briefly here, for when they journeyed from Elim, they pitched by the Red Sea, and they journeyed from the Red Sea, and they pitched in the wilderness of Sin,²⁷⁷Numbers 33:10-11. since this great wilderness extended from Elim to Sinai. Thus, when they travelled from Elim, they camped beside the Red Sea in that wilderness. Then they journeyed from the edge of the sea and entered into the midst of the wilderness, making the stages of Dophkah and Alush,²⁷⁸Ibid., Verses 12-13. See Ramban further at beginning of Seder Yithro (Note 25) for how this explanation affects a major problem in Torah exegesis as to when Jethro came, i.e., before or after the Giving of the Torah. and then they journeyed from Alush, which is in the wilderness of Sinai, and they pitched in Rephidim.²⁷⁹Ibid., Verse 14.
In the opinion of our Rabbis,²⁸⁰Shemoth Rabbah 25:5. the manna began falling in Alush. When the Israelites saw that they were journeying and camping in the wilderness — in Dophkah and Alush — and had not come out of it, they became frightened and began murmuring. This is the meaning of the verse, And they murmured… in the wilderness,²⁸¹Verse 2. for they had not murmured when they came there but only after they were there in the wilderness [for an extended period of time].

בחמשה עשר יום לחודש השני, this was the day when they ran out of the unleavened bread they had flung over their shoulders as dough when they left Egypt.