Shemot 3:18

18 And they shall pay heed to thy voice; and thou shalt go, thou and the Ziknei Yisroel, unto Melech Mitzrayim, and ye shall say unto him, Hashem Elohei HaIvriyim hath met with us; and let us go, now, derech shloshet yamim into the midbar, that we may sacrifice to Hashem Eloheinu.