Valmiki Ramayana Ayodhya Kanda Sarga 105 Shloka 31

स्रोतसो वा like the flow, अनिवर्तिनः never returns, वयसः of age, पतमानस्य while declining, आत्मा mind, सुखे in happiness (in the righteous act as source of hapiness), नियोक्तव्यः is to be established, प्रजाः people, सुखभाजः tend to be happy, स्मृताः it is said.

Like the flow of water which never reverts to its source, age passes. Therefore, a man must employ his self in righteous acts that bring him happiness. By doing so, it is said, people will always be happy.