Valmiki Ramayana Yuddha Kanda Sarga 63 Shloka 25
Original Shlokaअस्मिन्कालेतुयद्युक्तंतदिदानींविधीयताम् । गतंतुनानुशोचन्तिगतंतुगतमेवहि ।।6.63.25।।
1 source checked for this shloka
अस्मिन् that alone, काले time, यत् that, युक्तम् which is proper, तत् that, इदानीम् to do now, विधीयताम् you may speak, गतम् past, न अनुशोचन्ति not think of again, गतम् past, गतमेवहि is past.
"You may speak of only what is proper to do now. Do not think of the past as it is gone."