Shiva Purana
सवर्णायाश्च गमनं गुरुभार्य्यासमं स्मृतम् ॥ महापापानि चोक्तानि शृणु त्वमुपपातकम् ॥ ४०॥
It is considered equal to the wife of a preceptor to go to a woman of the same caste I have also described the great sins and hear the consequences.
english translation
savarNAyAzca gamanaM gurubhAryyAsamaM smRtam ॥ mahApApAni coktAni zRNu tvamupapAtakam ॥ 40॥
hk transliteration by Sanscript