The rat had been clinging to debris as it struggled to stay afloat in the pond in Lucknow, in northern India, and welcomed the assistance of a more aquatic creature.
The friendship is reminiscent of The Wind in the Willows, the beloved children's book in which Ratty helps Mr Toad reclaim his ancestral home.
'I had parked my scooter on the shore near the pond,' he said. 'I noticed something floating and soon realised it was the rat holding onto some piece of debris.
'It was as if the two creatures were talking in their own way. The next moment, the rat managed to climb onto the back of the frog.
'All this happened very fast. I quickly reached for my bag and took out my camera.'
The frog proceeded to dive into the water, carrying his passenger on the back, and made it to the shore.
Mr Husain said: 'I managed to take a few pictures. I was fascinated with the way the frog swam and the rat held on tight. They were like friends.
'Sadly, I could not catch the moment when the frog reached the shore and rat just sped away.
'I looked around for a bit but both the little creatures had just gone back to their world.'