Parashas Naso
וְאִ֥ישׁ אֶת־קֳדָשָׁ֖יו ל֣וֹ יִהְי֑וּ אִ֛ישׁ אֲשֶׁר־יִתֵּ֥ן לַכֹּהֵ֖ן ל֥וֹ יִהְיֶֽה׃ {פ}
And each shall retain his sacred donations: each priest shall keep what is given to him.
Torah Temimah points to R’ Yochanan — TT (verified).
לו יהיו — א״ר יוחנן: כל שיש לו תרומות ומעשרות ואינו נותנן לכהן, סוף שנצרך להן.
English: “It shall be his” — R’ Yochanan said: Anyone who has terumos and maasros and does not give them to the kohen will ultimately need them [himself].
Custom
Chazal warn that one who withholds terumah and maaser will eventually find himself in need of those very gifts.