Skandapurana 5.30

The seers said:
By which Siddha was the all-pervading lord Siddheśvara propitiated there? / Explain all this in detail, O delight of Sūta.

Sūta said:
Formerly, there was a lord of the Siddhas known by the name of Haṃsa; / because he was childless, a great amount of time passed for him.

Then, seized by sorrow, he went to the priest of the gods, / the son of Aṅgiras, the best of brahmins, Bṛhaspati, and asked him:

“O venerable one, old age has arrived for me, and I am childless; / therefore, proclaim to me the means for obtaining offspring,

a pilgrimage to sacred fords, a vow, or a propitiatory rite, O best of the twice-born, / by which progeny may quickly come about through your grace, O Bṛhaspati.”

After meditating for a long time, Bṛhaspati then said to the Siddha: / “Go to the sacred field of Camatkārapura and perform austerity there.

Then you will obtain an auspicious, noble son capable of uplifting your lineage; / O lord of Siddhas, I see no other auspicious means for [gaining] a son.”

Then, having reached that sacred field, that Siddha, endowed with faith, / himself worshipped the liṅga according to the prescribed rules.

Unwearied by day and night, he then worshipped [it] / with offerings of food, worship, gifts, and the performance of vocal and instrumental music.

By means of cāndrāyaṇa penances, kṛcchra penances, and parāka penances, O best of the twice-born, / and by fasts lasting for a month, he propitiated Śaṃkara.

Then, after two thousand years, Maheśvara was pleased with him; / mounted on a bull along with Umā, he went into his vision and said:

“O Haṃsa, today I am pleased with you; therefore, ask for what you desire; / I shall certainly grant it to you, even if it is difficult to attain.”

Haṃsa said:
“Formerly, an undertaking for the sake of offspring was initiated by me; / therefore, grant me sons capable of uplifting my lineage, O lord.

And you must always remain here in this liṅga, O best of the gods, / undoubtedly at my request, for the sake of the welfare of all the worlds.”

The Holy Lord said:
“From this day forward, my dwelling will be in this liṅga / at your word, O lord of Siddhas; this which has been spoken by me is the truth.

Whatever mortal will worship me residing here with devotion, / to him I will give all the fruit abiding in his heart.

Whoever, standing in the southern direction of my liṅga, will recite the mantra / of six syllables, to him I will give long life accompanied by sons.”

Having spoken thus, the great god then disappeared from sight; / and Haṃsa, having returned home, obtained highly prosperous sons.

Therefore, by every effort, that liṅga should be carefully touched, / worshipped, and saluted with diligence, O twice-born,

and celebrated according to one's power with the six-syllable mantra / by those who desire desired objects, which are difficult even for the thirty gods to attain.

Thus ends the thirtieth chapter, titled ‘Description of the Account of the Origin of Siddheśvara,’ in the Māhātmya of the Sacred Field of Hāṭakeśvara, in the Nāgarakhaṇḍa, the sixth [section], in the eighty-one-thousand-verse collection of the glorious Skanda Mahāpurāṇa.