How can I "unshift" a 1D array into each el of a 2D array?

Question

Given ar1, how can I iterate through ar2 and unshift() ar1 having this repeated at the beginning of a2 as a result?

let ar1 = [4, "Purchase Order", "Yoga"];
let ar2 = [
  ["221123-B", 1, "006"],
  ["221123-C", 1, "006"],
  ["221123-D", 1, "006"],
  ["221123-E", 1, "006"]
]

ar2.forEach(function(el, i) {
  el = ar2[i].unshift(ar1)
})
console.log(JSON.stringify(ar2));

Expected Result:

[
  [4, "Purchase Order", "Yoga", "221123-B", 1, "006"],
  [4, "Purchase Order", "Yoga", "221123-C", 1, "006"],
  [4, "Purchase Order", "Yoga", "221123-D", 1, "006"],
  [4, "Purchase Order", "Yoga", "221123-E", 1, "006"]
]