TT #422 · Parashas Reeh · Seventh Aliyah · Passuk 16:16
Three times in the year all your males shall appear before Hashem your God in the place that He will choose: on the festival of Matzos, on the festival of Shavuos, and on the festival of Sukkos; and they shall not appear before Hashem empty-handed.
Torah Temimah points to Rosh Hashanah / Chagigah.
Sefaria — Rosh Hashanah / Chagigah
English: "On the festival of Matzos..." — from here we learn that one who is obligated in valuations, dedications, sin-offerings, guilt-offerings, burnt-offerings, peace-offerings, charity, tithes, the firstborn, the animal tithe, the Pesach, leket, shikhecha and pe’ah—once three festivals have passed over them—violates the prohibition of delaying.
Derash on the verse (Rosh Hashanah) — the three festivals and bal te’acher.
Once three pilgrimage festivals have elapsed, one who has not yet discharged certain vows and obligations violates the prohibition against delay.