Valmiki Ramayana Ayodhya Kanda Sarga 111 Shloka 21
Original Shlokaएषोऽपि हि महाभागः पितुर्वचसि तिष्ठति। अत एव न शक्ताः स्मो व्यावर्तयितुमञ्जसा।।2.111.21।।
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एषः this, महाभागः highly distinguished Rama, पितुः father's, वचसि word, तिष्ठति हि is fixed, अत एव that is why, अञ्जसा quickly, व्यावर्तयितुम् to make him return, शक्ताः capable, न स्मः not.
Highly distinguished Rama is firmly fixed on the command of his father. That is why we are incapable of making him return quickly.