स्कन्दपुराणम्/खण्डः १ (माहेश्वरखण्डः)/केदारखण्डः/अध्यायः ०८
https://sa.wikisource.org/s/gysIn this Purana, Maha Vishnu said in connection with Ramavatara: Let the gods take the form of monkeys and incarnate on earth for the fulfillment of Rama's mission:
एवं संभाष्य भगवान्विष्णुः परममङ्गलः॥
वाली चेन्द्रांशसंभूतः सुग्रीवोंशुमतः सुतः॥ ८.९८ ॥
Vaali incarnated from the Indra element and Sugriva came as the son of Surya.
तथा ब्रह्मांशसंभूतो जाम्बवान्नृक्षकुञ्जरः॥
शिलादतनयो नंदी शिवस्यानुचरः प्रियः॥ ८.९९ ॥
Jambavan, who is Brahmamsha, incarnated as a Vanara and became the minister of Sugriva.
Nandikeshwara (son of Shilaada), servant of Shiva, admirer of Shiva, the eleventh Rudra, incarnated as Hanuman, to be of service of Vishnu (Rama):
यो वै चैकादशो रुद्रो हनूमान्स महाकपिः॥
(In the reading of Sri Appaiah Dikshitar : एकांशेन महाबाहो हनुमान्स महाकपिः )
अवतीर्णः सहायार्थं विष्णोरमिततेजसः॥ ८.१०० ॥
Even the Valmiki Ramayana gives us a hint about this:
किमेष भगवान्नन्दी भवेत्साक्षादिहागतः || ५-५०-२.२
येन शप्तोऽस्मि कैलासे मया संचालिते पुरा | ५-५०-३.१
On seeing Hanuman, Ravana remembers the curse of Lord Siva (Nandi) on him that he would perish when a monkey resembling Siva strikes him! He doubts if it was Nandi the chief of Pramatha ganas of Siva with a monkey face.
This is what Sri Appaiah Dikshitar has said in his own commentary to his 'Sri Ramayana Tatparya Sara Sangraha Stotra', with evidence.
In the same chapter it is said that Vishnu is a form of Shiva:
विष्णुना हि महाभागास्तस्मात्सर्वं विधास्यति॥ ८.८४ ॥
देवदेवो महादेवो विष्णुरूपी महेश्वरः॥
It is also said that Vishnu himself incarnated as Rama 'endowed with ignorance':
हे देवाः श्रूयतां वाक्यं प्रस्तावसदृशं महत्॥
शैलादिं च पुरस्कृत्य सर्वे यूयं त्वरान्विताः॥
अवतारान्प्रकुर्वन्तु वानरीं तनुमाश्रिताः॥ ८.९४ ॥
अहं हि मानुषो भूत्वा ह्यज्ञानेन समावृतः॥
संभविष्याम्ययोध्यायं गृहे दशरथस्य च॥
Om