In the chapter 24-25, Section 3 of Satarudra Samhita of Shiva Purana, the story of incarnation of Shiva as Pippalada is mentioned.
There was a great brahmin and an excellent sage, Daddichi. He was born of Cyavana of Bhṛgu family. He was a great devotee of Shiva and very powerful. In the fight with Kṣuva, Vishnu and other gods were defeated by this sage who had the support of Shiva and they were cursed. His wife Suvarca was very noble and chaste. The gods were cursed by her. Pippalada, an expert in different kinds of sports and extremely brilliant was born of her.
Once Indra and other gods were defeated by the Daityas who had the support of the demon Vṛtra.
Then the harassed gods and the sages along with Indra immediately went to Brahma’s region and narrated their distress to him. On hearing the words of the gods Brahma, mentioned the details of what Tvaṣṭṛ was desirous of doing. This Asura has been created by Tvaṣṭṛ by means of his penance in order to kill you. The name of that Asura is Vṛtra. He is of great brilliance and the leader of all Daityas.
Brahma said, “There is a great sage Dadhīci of great penance and of full control of his sense-organs. After propitiating Shiva, he secured the boon of adamantine bones formerly. You all request for his bones. He will undoubtedly give them to you. Make the thunderbolt staff therewith and kill Vṛtra without hesitation.”
Indra accompanied by his preceptor and other gods went immediately to the excellent hermitage of Dadhici. They asked him with great reverence to give his bones of adamantine strength. The sage fond of helping others meditated on lord Shiva and abandoned his body. Immediately he reached Brahma’s region with his bondage of actions quashed. Indra then called the divine cow Surabhi to lick up the marrow etc. He directed Viśvakarman to make the weapon with the bones.
At his behest Vishvakarman made all the weapons with the sage’s bones—very firm and adamantine—that had the brilliance of Shiva. With his backbone he made the thunderbolt, arrow and the missile called Brahmashiras. With the other bones he made many other weapons. The infuriated Indra lifted the thunderbolt and rushed against Vṛtra like Rudra rushing against the god of death. Indra who was well prepared, cut off the peak like head of Vṛtra with the thunderbolt forcefully.
The chaste lady, Suvarca, desirous of attaining the world of her husband sat down and broke open her belly with a stone. The foetus of the child of the great sage! of brilliant divine body, came out. The great chaste lady became delighted, bowed to him and eulogised him. The chaste lady Suvarca followed her husband by means of the great transcendental meditation. Thus, the wife of Dadhici was re-united with her husband. After reaching Shiva’s region she served Shiva devotedly. The delighted Brahma named him Pippalada. Viṣhṇu and the gods said “O lord of the gods be pleased”. Then Rudra, the great lord in the form of Pippalada, performed a penance for a long time at the foot of the fig tree, with a desire to bestow benefit on the worlds. As Pippalada, following the convention of the world, performed the penance, a long time passed by.
After arranging and establishing Dharma with a desire for its good foundation, lord Shiva performed great sports. Once while going to the river Puṣpabhadra for his ablution, the great sage saw the beautiful youthful maiden Padma, a part of Shiva herself. Desirous of getting her, the sage traversing the world and an expert in following the established conventions went to the abode of king Anaraṇya, her father. On seeing him, the king bowed to him. The sage requested for the hand of his daughter. Thereupon the king was unable to say anything. He was silent. The sage repeated the request, saying “Give me your daughter devoutly. Otherwise, I will reduce everything to ashes along with you.”
The king was much frightened. He gave his daughter Padma, fully bedecked in ornaments to the old sage. After marrying Padma, the daughter of the king and a part of Shiva, the sage Pippalada joyously took her to his hermitage. After going to the hermitage, the aged excellent sage stayed there with that woman. The sage was not too indulgent. The daughter of Anaraṇya served the sage with devotion. Then the excellent sage Pippalada became a young man by means of his divine sport and sported with that young lady. Ten noble sons, all of them great sons, were born to the sage. They were equal to their father and increased the pleasure of Padma.
On seeing the harassment by the planet Saturn of every one irremediably, the sympathetic lord lovingly granted a boon to all the world. “For sixteen years from birth no man will have that affliction. Similarly, to the devotees of Shiva too. If Saturn were to disregard my instruction and harass men, he will undoubtedly be reduced to ashes.” Thus, afraid of him the excellent planet Saturn, though in aberration, does not afflict men at any time.