Ramayana
न मिथ्या ऽहं वदे राम देवलोकजिगीषया । शूद्रं मां विद्धि काकुत्स्थ तप उग्रं समास्थितम् ॥ 7-76-3 ॥
I do not speak falsely, O Rama, out of my desire to conquer the world of the gods. Know me, O Kakutstha, to be a Shudra who has undertaken this fierce penance."
english translation