This question is about these images:
This incident (depicted) happened after Lord Buddha visited a certain Deva realm.
- Can someone provide any sutta or sutra reference?
- If you can, please explain the event and the drawings?
One of those pictures is shown on this page: Lhabab Duchen – the Day Buddha Descended from Tushita Heavens:
This article from Bhutan Journals describes the iconography of the Buddha Shakyamuni Descending from Tushita Heavens to the Earth.
A version of this story is told/included in the Dhammapada-aṭṭhakathā (verse 181):
On return from the Tavatimsa deva world, the Buddha uttered Verse (181) of this book at Sankassanagara, in reply to Thera Sariputta's words of welcome.
There's a more detailed version of this story somewhere else (I don't know where), for example Wikipedia's Lhabab Duchen article includes details about a "triple ladder" (shown in all the pictures):
He was exhorted by his follower and representative Maudgalyayana to return, and after a long debate and under a Full Moon agreed to return. He returned to earth a week later by a special triple ladder prepared by Viswakarma, the god of machines. This event is considered to be one of the eight great deeds of the Buddha.