It's an old English custom/saying meant to bring good luck! You have to say out loud three times as the very first thing you say on the first day of each month. My mum instilled the habit, and still messages me first thing in the morning every first of the month with three "white rabbits". I do try to say it first thing every month 🐇🐇🐇.

Edit: my mum is also into numerogy/astrology, and apparently today especially is extra lucky for both me and her in numerology - she's buying a lotto ticket and so am I!

Edit2: apparently the draw number 4699 makes it even luckier still 😂