Not a word does he (or she) utter, but there is a

﴿مَّا يَلۡفِظُ مِن قَوۡلٍ إِلَّا لَدَيۡهِ رَقِيبٌ عَتِيدٞ ﴾
[قٓ: 18]

Not a word does he (or she) utter, but there is a watcher by him ready (to record it)

﴿ما يلفظ من قول إلا لديه رقيب عتيد﴾ [قٓ: 18]

Al Bilal Muhammad Et Al
Not a word do they utter, except that there is with him a ready observer

Ali Bakhtiari Nejad
He does not speak a word unless there is an observer with him ready (to record)

Ali Quli Qarai
he says no word but that there is a ready observer beside him

Ali Unal
Not a word does he utter but there is a watcher by him, ever-present

Hamid S Aziz
He utters not a word but there is by him a watcher (sentinel, one who censors) at hand

John Medows Rodwell
Not a word doth he utter, but there is a watcher with him ready to note it down

Literal
Nothing emits/vocalizes from a word except at Him (is a) prepared/made ready observer/guard

Mir Anees Original
he does not utter a word but one vigilant near him is ready

Mir Aneesuddin
he does not utter a word but one vigilant near him is ready