Proverbs 27:1 (BSB)

Do not boast about tomorrow, for you do not know what a day may bring.

From Proverbs 27. Also in the ESV.

Commentary on Proverbs 27:1

• Geneva Bible Notes (Reformed), Geneva Bible Study Notes on Proverbs 27:1: Boast not thyself of to morrow; for thou knowest not what a day may bring forth. (a) Do not delay the time, but take the opportunity when it is offered.
• Keil & Delitzsch (Lutheran), Biblical Commentary on the Old Testament on Proverbs 27:1: Pro 27:1 In the group Pro 27:1-6 of this chapter every two proverbs form a pair. The first pair is directed against unseemly boasting: 1 Boast not thyself of to-morrow, For thou knowest not what a day bringeth forth. The ב of בּיום is like, e.g., that in Pro 25:14, the ב of the ground of boasting.