Rashi on Numbers 15:33/רש"י על במדבר ט״ו:ל״ג

1המצאים אתו מקשש THEY THAT FOUND HIM PICKING UP WOOD — [The redundancy of the phrase המצאים אתו מקשש עצים intimates that] they warned him not to do this and yet he did not refrain from picking them up even after they had found him and warned him (cf. Sifrei Bamidbar 113; Sanhedrin 41a).