Boasting is to speak with excessive pride and self-satisfaction about one's achievements, possessions, or abilities.
Boasting is generally a blameworthy attribute that a God-fearing person should not exhibit in his character or speech.
Imam 'Ali b. Abi Talib (a) has several short sayings addressing this behaviour of pride and boastfulness.
1. What reason has a human being to be proud when his beginning is a drop of semen and his end is a carcass; neither can he sustain himself nor can he repel his [own] death!
2. Never become proud of a state that you attained without [any] device [and hard work], and never be arrogant of a rank that you attained without merit, for indeed that which is built by circumstance is destroyed by entitlement.
3. There is no foolishness greater than arrogance.
4. Boasting ought to be about the greatest effort, keeping promises and being overly generous, not about the worn out bones [of one’s ancestors] and evil traits.
5. Boastfulness stems from the smallness of [one’s] status [and worth].
6. Beware of contesting with Allah, the Glorified, in His greatness, for Allah, the Most High, abases every tyrant and belittles every boaster.
Source - Ghurar al-hikam wa durar al-kalim
You can find these sayings with their original arabic here - https://www.al-islam.org/ghurar-al-hikam-wa-durar-al-kalim-exalted-aphorisms-and-pearls-speech/pride-and-boasting