Valmiki Ramayana Ayodhya Kanda Sarga 22 Shloka 24

इह here, आरब्धम् undertaken, आरम्भम् initiation, निवर्त्य having stopped, असङ्कल्पितम् एव unanticipated, अकस्मात् suddenly, यत् such hindrance, प्रवर्तते takes place, तत् that one, दैवस्य destiny's, कर्म ननु is the result of action.

Any unanticipated and sudden hindrance to the action undertaken shall be deemed to be the act of destiny.