Mudgalapurana 5.45.5

5.45.5

asya śrīgaṇeśakīlakasya |
śiva ṛṣiḥ |
anuṣṭup chandaḥ |
śrīgaṇapatirdevatā |
oṃ gaṃ yogāya svāhā |
oṃ gaṃ bījam |
vidyā'vidyāśaktigaṇapatiprītyarthe jape viniyogaḥ |
chandaṛṣyādinyāsāṃśca kuryādādau tathā parān |
ekākṣarasyaiva dakṣa ṣaḍaṅgānācaret sudhīḥ ||

Of this glorious pin of Gaṇeśa:
Śiva is the seer;
the meter is Anuṣṭubh;
the deity is the glorious Gaṇapati;
"Oṃ gaṃ yogāya svāhā";
"Oṃ gaṃ" is the seed-syllable;
the ritual application in repetition is for the pleasure of Gaṇapati, who has the power of knowledge and ignorance.
O Dakṣa, the wise person should first perform the installations of the meter, the seer, and the rest, and then the other [installations];
he should perform the six-limb installation of the single-syllable mantra itself.