Original text
ॐ आञ्जनेयाय विद्महे वायुपुत्राय धीमहि। तन्नो हनुमत् प्रचोदयात्॥
Transliteration
Om Anjaneyaya Vidmahe Vayuputraya Dhimahi, Tanno Hanumat Prachodayat.
The Gayatri pattern applied to Hanuman
Many deities have their own "Gayatri" mantra built on the same three-part structure as the classical Gayatri Mantra to the sun: an address ("we know/meditate on..."), a further description of the deity, and a closing request to inspire the devotee's understanding (dhi). This version addresses Hanuman as Anjaneya (son of Anjana) and Vayuputra (son of the wind), asking him to illuminate and inspire the devotee's mind.
Other versions worth knowing
Some sources give slightly different second lines, invoking Hanuman as Ramaduta (Rama's messenger) or Kapiraja (king among vanaras) instead of Vayuputra — a normal feature of Gayatri-pattern mantras across deities, where regional or lineage-based variants exist without one being more "correct" than another.
How it's chanted
Like other Gayatri-pattern mantras, it's typically chanted 108 times on a mala, ideally at sunrise or another quiet moment, and is considered particularly suitable for students, those seeking clarity of mind, or anyone wanting Hanuman's protection during travel.