Valmiki Ramayana Bala Kanda Sarga 24 Shloka 18

राम O Rama, पुरा in ancient times, वृत्रवधे at the time of destruction of Vritrasura, मलेन by impurity, क्षुधा चैव by hunger also, समभिप्लुतम् overpowered, सहस्राक्षम् Indra, ब्रह्महत्या sin arising out of slaying Brahmin, समाविशत् attacked.

O Rama, in ancient times after killing Vritrasura, Indra was overpowered by the sin of slaying a brahmin and was affected by impurity and hunger.