Shiva Purana
सुदर्शनाय पुत्राय ददौ प्रीत्या तदाम्बिका ॥ उद्दिश्य शिवगायत्रीं षोडशाक्षरसंयुताम् ॥ ४३ ॥
Ambika lovingly gave it to her son Sudarsana Addressing the Shiva Gayatri composed of sixteen syllables.
english translation
sudarzanAya putrAya dadau prItyA tadAmbikA ॥ uddizya zivagAyatrIM SoDazAkSarasaMyutAm ॥ 43 ॥
hk transliteration by Sanscript