Bhagavad Gita 18.37
Which at first seems like poison but afterwards acts like nectar—that pleasure is pure, for it is born of wisdom.
यत्तदग्रे विषमिव परिणामेऽमृतोपमम्।तत्सुखं सात्त्विकं प्रोक्तमात्मबुद्धिप्रसादजम्॥yattadagre viṣamiva pariṇāme'mṛtopamam|tatsukhaṃ sāttvikaṃ proktamātmabuddhiprasādajam||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).