Valmiki Ramayana Bala Kanda Sarga 1 Shloka 35

आर्यभावपुरस्कृत: worshipped with reverence, सुमहात्मानम् highly respectable, सत्यपराक्रमम् truthful chivalry, गत्वा having reached, रामम् Rama, भ्रातरं रामम् brother Rama, अयाचत् implored. धर्मज्ञ: knower of righteousness, त्वमेव you alone, राजा इति should be the king, रामम् addressing Rama, वच: words, अब्रवीत् spoke.

Bharata reached Rama, so pleasing venerable, truthful and chivalrous, worshipped him with reverence and implored. Bharata addressing Rama said, 'You are knower of righteousness. You alone should be the king (meaning that when the elder brother is alive, the younger brother is prohibited from ruling the kingdom)'.