Psalm 121:3 New English Translation

³May he not allow your foot to slip.
May your Protector^[a] not sleep.^[b]

Psalm 121:3 tn Heb “the one who guards you.”
Psalm 121:3 tn The prefixed verbal forms following the negative particle אַל (ʾal) appear to be jussives. As noted above, if they are taken as true jussives of prayer, then the speaker in v. 3 would appear to be distinct from both the speaker in vv. 1-2 and the speaker in vv. 4-8. However, according to GKC 322 §109.e), the jussives are used rhetorically here “to express the conviction that something cannot or should not happen.” In this case one should probably translate, “he will not allow your foot to slip, your protector will not sleep,” and understand just one speaker in vv. 4-8. But none of the examples in GKC for this use of the jussive are compelling.

New English Translation (NET)