This verse (chaupai) is from the Sundarkanda chapter of Shri Ramcharitmanas.

प्रबिसि नगर कीजे सब काजा। हृदयँ राखि कोसलपुर राजा॥ गरल सुधा रिपु करहिं मिताई। गोपद सिंधु अनल सितलाई॥
Context: where this chaupai appears in Shri Ramcharitmanas
In Sundarkanda, after leaping across the ocean, Hanuman ji reaches the gate of Lanka, where the demoness Lankini stops him. Overwhelmed by a single blow from him, she recalls Brahma ji's words and herself says: enter the city and do all your work, keeping Shri Ram, the King of Kosalpur (Ayodhya), in your heart. For one who carries Shri Ram in the heart, poison becomes nectar, enemies turn into friends, the ocean shrinks to a cow's hoofprint, and fire turns cool.
Transliteration
Prabisi Nagar Kije Sab Kaja. Hridayan Rakhi Kosalpur Raja.. Garal Sudha Ripu Karahin Mitai. Gopad Sindhu Anal Sitalai..
Word meanings
- Prabisi = having entered
- Kaja = work, tasks
- Hridayan rakhi = keeping in the heart
- Kosalpur raja = Shri Ram, King of Ayodhya
- Garal = poison
- Sudha = nectar
- Ripu = enemy
- Mitai = friendship
- Gopad = a cow's hoofprint
- Sindhu = ocean
- Anal = fire
- Sitalai = coolness
As a Shalaka answer
This is a highly auspicious answer. Begin the work with remembrance of the Lord; obstacles will turn favourable on their own, just as every barrier of Lanka became a path for Hanuman ji.