For each row, I have text in 3 columns that I want to concatenate into one
cell with a return after each line.

Example, given a row with the following...

A1 - "This is"
A2 - "my"
A3 = "sample date"

I'm trying to write a concatenate formula so that the contents of each
source cell (A1 thru A3) appears on a line by itself, but all within a single
cell so the output is:

This is
my
sample data

How do I concatenate text with a new line code?