Shiva Purana
पराशरेण संयोगः पुनः शन्तनुना यथा ॥ सत्यवत्या इव ब्रह्मन्नः संशयितुमर्हसि ॥ १३८ ॥
O brahmin, you shall not entertain a doubt as to why Satyavatī had sexual intercourse with Parāśara and Śantanu.
english translation
parAzareNa saMyogaH punaH zantanunA yathA ॥ satyavatyA iva brahmannaH saMzayitumarhasi ॥ 138 ॥
hk transliteration by Sanscript