Potential employer asking for a writing sample – Info Career Dev

Hello

I applied to a grassroots organization that is directly involved in helping refugees back home. Position is a intern and from why I understood the focus for this role is grant writing.

The length was not specified but I was asked for a few samples. Never written a writing sample before for a job, should I writr one or share a excerpt from a proposal I did at my previous work?

Any advice is significantly helpful.

Thank you