[1] The early medieval master Hai Gaon notes a method for attaining a dream question involving fasting, purification, and meditation on a text.
Based on comments by Abraham ibn Ezra and others, scholar Moshe Idel has identified this text with Exodus 14:19-21, each verse of which contains 72 consonants alluding to a mystical series of Hebrew letters said to represent the true name of God.
In his work "On "She’elat Halom" in “Hasidei Askenaz: Sources and Influences",[2] Idel points to Chagigah 5b[3] in the Babylonian Talmud where God made a promise to the people of Israel, that despite being hidden from view, he will speak to them in dreams.
The Process of She'elat Halom Hai ben Sherira Gaon, a medieval Jewish Rabbi and scholar living from 939 to 1038, recounted experiences of elders confronting the dream question.
[2] In their autobiographical writings from the early 17th century, both mystic Hayyim Vital and rabbi Leon of Modena claim matter-of-factly to have asked a dream question.
The Gematria of the 17 initial letters (or Reshei Tevot) adds up to be 597 which is also the numerical value of the phrase combining the Hebrew words for prophecy, the name of God, and spirit guide.