Ganapati Gayatri Mantra | In which Shastra it is contained this mantra and who wrote it firstly?

Question

This very mantra for Shree Ganesha

Who wrote it for first?

Which Shastra- Veda or others- contain that?

Dhanyawaad Thank you

https://www.thedivineindia.com/ganpati-gayatri-mantra/5889

Answer 1

The mantra you are referring to (the one that is found the link given in the question) is Ganapaty Gayatri mantra viz:

Aum Ekadantaya Viddhamahe, Vakratundaya Dhimahi, Tanno Danti Prachodayat॥

It is originally from the Mahanarayana Upanishad. The Upanishad has a separate section containing Gayatri mantras of various deities.

गायत्र्याः ।

तत्पुरुषाय विद्महे महादेवाय धीमहि । तन्नो रुद्रः प्रचोदयात् ॥ २३॥ (tatpurushaya vidmahe mahadevaya dhimahi | tanno rudrah prachodayat ||)

तत्पुरुषाय विद्महे वक्रतुण्डाय धीमहि । तन्नो दन्तिः प्रचोदयात् ॥ २४॥ (tatpurushaya vidmahe vakratundaya dhimahi | tanno dantih prachodayat ||)

The Upanishad is associated with Krishna Yajurveda. And, Upanishads don't have authors.

Answer 2

Ganapati Gayatri Mantra is found in Ganapati Atharvashirsha Upanishad.

Credits: Commentary on Ganapati Atharvashirsha Upanishad by Swami Tejomayananda

Edit: The mantra referred to in the link is correctly addressed by Rickross.