Ask, and I will give you

Rabi'ah ibn Ka'b spent his nights near the Prophet ﷺ, bringing him water for his ablution and for the night prayer, and attending to whatever else came up. It was not a formal arrangement. He simply stayed close and made himself useful.

One time, the Prophet ﷺ told him to ask for something, and he would give it to him.

Rabi'ah did not ask for money, or for land, or for anything of this world. He asked to remain the Prophet's ﷺ companion in Paradise.

The Prophet ﷺ asked if there was anything else. Rabi'ah said that was all he wanted.

He was then told that he could help bring that about for himself — by increasing how much he prostrated in prayer.

That is the whole exchange, and it is preserved in Sahih Muslim. A man who had almost nothing of his own was given the chance to ask for anything, and asked for the one thing that could not be bought or inherited.