Lord Vishnu received a curse from one of His most loyal devotees. The curse turned Him into a stone.
Who is he/she? What is the reason for Cursing God?
Do any Scriptures mention this Curse?
Yes. It was Tulasi who cursed Vishnu to become Saligrama Stone and Tulasi became Gandhaki River and Tulasi plant. Saligrama Stone is Swayambhu representation of Lord Vishnu and one gets many virtues by worshiping it.
Story of Tulasi and Shamkachuda is described in detail from Chapter 27 to Chapter 41 of Rudra Samhita (Yuddha Khanda) of Shiva Mahapurana, from Chapter 17 to Chapter 25, Ninth canto of Devi Bhagavatam and from Chapter 15 to 22 of Prakriti Khanda of Brahma Vaivartara Purana . I will answer this question from Shiva Purana but Devi Bhagavatam and Brahma Vaivartara Purana also says the same.
Tulasi was cowherdess in Golaka (Krishna's Loka) and ardent devotee of Sri Krishna .Radharani cursed Tulasi to get born in country of Bharata and Sudama was born as danava Sankhachuda.
Samkhachuda performs Tapasya for Brahma and gets Krishna Kavacha. Chapter 28 says:
वरं ययाचे ब्रह्माणमजेयत्वं दिवौकसाम्।
तथेत्याह विधिस्तं वै सुप्रसन्नेन चेतसा।। ५ ।।
श्रीकृष्णकवचं दिव्यं जगन्मङ्गलमङ्गलम्।
दत्तवाञ्शङ्खचूडाय सर्वत्र विजयप्रदम्॥६॥
He asked for a boon from Brahma, that he should be invincible from the gods. Brahma, getting pleased said to him, "Be it so.” For this purpose he gave him away the Krsna-kavaca which bestowed welfare on the universe and made the holder victorious everywhere.
Samkachuda later marries Tulasi and develops enmity towards Devas listening words of Sukracharya.
During war, divine voice of Brahma (akasavani) says due to kavacha and chastity of his wife Tulasi, Shiva and Devas couldn't kill Samkachuda. Chapter 40 says:
यावदस्य करेऽत्युग्रं कवचं परमं हरेः।
यावत्सतीत्वमस्त्येव सत्या अप्यस्य योषितः ।। १२।।
तावदस्य जरा मृत्युः शडुचूडस्य शडूर!।
नास्तीत्यवितथं नाथ! विधेहि ब्रह्मणो वचः।। १३।।
Till such time the demon carries in his hand the kavaca of Visnu, and till such time the chastity of his wife is preserved, Samkhacuda could neither become old no meet with his death. These are the truthful words of Brahma.
So, Vishnu turns into a Brahmana and asks Kavacha from Samkhachuda and destroys chastity of Tulasi and thereafter Shiva kills demon Shamkachuda with ease.
When Tulasi was lamenting, Shiva manifests there and explains everything to Tulasi. Chapter 41 says:
मा रोदीस्तुलसि! त्वं हि भुङ्क्ते कर्मफलं जनः।
सुखदु:खदो न कोऽप्यस्ति संसारे कर्मसागरे॥ ४०॥
Siva said, “O Tulasi, do not lament, Everyone has to reap the reward of his actions. In the ocean of karmas in this World, there is nothing like the pleasure and the pain.
तपस्त्वया कृतं भद्रे! तस्यैव तपसः फलम्।
तदन्यथा कथं स्याद्वै जातं त्वयि तथा च तत्॥ ४२॥
O Tulasi, you discarding this body shall achieve the divine body. Then you taking to the form of Laksmi, would enjoy the company of Visnu daily.
इदं शरीरं त्यक्त्वा च दिव्यदेहं विधाय च।
रमस्व हरिणा नित्यं रमया सदृशी भव॥४३॥
Discarding this body, when you take to the divine form, then you would enjoy the company of Visnu, like LakSmi.
तवेयं तनुरुत्सृष्टा नदीरूपा भवेदिह।
भारते पुण्यरूपा सागण्डकीति च विश्रुता॥४४॥
When your body comes to an end, then you would be known as the auspicious river Gandaki in Bharata.
कियत्काल महादेवि! देवपूजनसाधने। प्रधानरूपा तुलसी भविष्यति वरेण मे॥४५॥
O Great goddess, because of my boon, for a long time you would become the means for the adoration of the gods
। स्वर्ग मत्यें च पाताले तिष्ठ त्वं हरिसन्निधौ।
भव त्वं तुलसीवृक्षो वरा पुष्पेषु सुन्दरी।। ४६॥
You would always keep the company of Visnu in the heaven, earth and Patala. O Beautiful one, among the flowering trees, you would become the beautiful Tulasi plant.
हरिवै शैलरूपी च गण्डकीतीरसन्निधौ।
सङ्करिष्यत्यधिष्ठानं भारते तव शापतः।। ४९॥
Lord Visnu, because of your curse to him, would remain on your banks in the form of StOne.
तत्र कोट्यश्च कीटाश्च तीक्ष्णदंष्ट्रा भयङ्कराः।
तच्छिक्त्वा कुहरे चक्रं करिष्यन्ति तदीयकम्॥५०॥
The crores of terrible sharp-toothed worms shall penetrate and erode the stones and carve rings on it.
शालग्रामशिला सा हि तड़ेदादतिपुण्यदा।
Because of the difference in the cakras, those stone will be termed as representing Laksmi-Narayana etc. and will be treated as auspicious and the bestower of the merits.
शालग्रामशिला विष्णोस्तुलस्यास्तव सङ्गमः।
सदा सादृश्यरूपा या बहुपुण्यविवर्धिनी। ५२॥
The Salagrama-sila of Visnu, and the confluence of Tulasi there, the place will enhance the merits.
तुलसीपत्रविच्छेदं शालग्रामे करोति य:।
तस्य जन्मान्तरे भद्रे! स्त्रीविच्छेदो भविष्यति॥ ५३॥
The one who removes the Tulasi-leaf (Holy basil) with Salagrama-sila, he will not face separation from his wife in the next birth.
Shiva also explains greatness of Saligrama stone and merits acquired by worshiping it in subsequent lines.
The story of the curse of Tulasi is enumerated in shlokas 23 -27, Ninth Canto Chapter 24 of Srimad Devi Bhagavatam. This English translation is from the English Translation by Swami Vijnanananda. Tulasi cursed Lord Vishnu as follows:
"O Lord! Thou art like a stone. Thou hast no mercy. By hypocrisy Thou hast destroyed my chastity, my virtue and for that reason didst kill my husband. O Lord! Thou had no mercy;
Thy heart is like a stone. So Let Thee be turned into a stone. Those who declare Thee as a saint, are no doubt mistaken. Why didst Thou for the sake of others, kill without any fault, another Bhakta of Thine. Thus speaking, Tulasî overpowered with grief and sorrow, cried aloud and repeatedly gave vent to lamentations."