Hi {{first_name}},
It's been a while since we worked together at [[company or institution]]. I hope things are going well on your end.
Since we last connected, I've been [[1-2 sentence career update]]. I'm now applying for [[program or role]] at [[institution or company]] and wanted to reach out before listing you as a recommender to see if you'd be comfortable with that.
If you're open to it, I'll send a prep note with everything you'd need. The deadline is [[date]].
Completely understand if the timing or distance makes this a tough ask.
[[Your name]]