Valmiki Ramayana Ayodhya Kanda Sarga 88 Shloka 26

अद्य प्रभृति from today, अहम् I, जटाचीराणि matted hair and robes made of bark, धारयन् wearing, नित्यम् always, फलमूलाशनः eating fruits and roots, भूमौ तु on the ground itself, तृणेषु वा or on the grass, शयिष्ये I will sleep.

From today onwards, wearing matted hair and clad in robes made of bark and living on fruits and roots, I too shall sleep on the naked ground or on grass.