Sforno on Deuteronomy 14:22/ספורנו על דברים י״ד:כ״ב

1עשר תעשר, for by tithing the crops of the fields and orchards as well as that of your livestock, you will actually increase their numbers (G’d will see to this) instead of decreasing the amount at your disposal. This is what our sages meant when they said in Shabbat 119 עשר בשביל שתתעשר, “give the tithes so that you will be enriched” (with the dot in the letter ש of the word תתעשר on the right hand side.).