Looking for a CS Lewis (?) quote

Its theme is something along the lines of “Christians always have time to spare for others” or “You will know a Christian because they will never be too busy for you”.

Just doing some recent reflection and having that concept rattling in the back of my brain really had a large impact on every important relation I’ve had in the past decade of my life

Would just like to revisit it so I can see exactly how it was worded

I have a hunch that it came from Mere Christianity or Screwtape Letters because I read both of those books as a teen, when I first came across the quote. But it might not even be CS Lewis to be honest.