Canto 2 -
Ayodhyā-kāṇḍa
Chapter 104: Bharata Beseeches Rāma to Rule the Kingdom
Text 2.104.6
स्त्रिया नियुक्तः कैकेय्या मम मात्रा परन्तप।
चकार सुमहत्पापमिदमात्मयशोहरम्॥
striyā niyuktaḥ kaikeyyā mama mātrā parantapa
cakāra sumahat-pāpam idam ātma-yaśo-haram
striyā = by a woman; niyuktaḥ = requested; kaikeyyā = Kaikeyī; mama = My; mātrā = mother; parantapa = O scorcher of enemies; cakāra = he committed; sumahat-pāpam = very great sin; idam = this; ātma-yaśaḥ-haram = that removed his reputation.
O scorcher of enemies, requested by a woman, My mother Kaikeyī, he committed this very great sin that removed his reputation.
The very great sin was banishing a good son to the forest