The word(s) "weaken" appears 3 time(s) in 3 verse(s) in Quran in Mohsin Khan translation.

(1) And many a Prophet (i.e. many from amongst the Prophets) fought (in Allah's Cause) and along with him (fought) large bands of religious learned men. But they never lost heart for that which did befall them in Allah's Way, nor did they weaken nor degrade themselves. And Allah loves As-Sabirun (the patient).

(2) This (is the fact) and surely, Allah weakens the deceitful plots of the disbelievers.

(3) Verily, Fir'aun (Pharaoh) exalted himself in the land and made its people sects, weakening (oppressing) a group (i.e. Children of Israel) among them: killing their sons, and letting their females live. Verily, he was of the Mufsidun (i.e. those who commit great sins and crimes, oppressors, tyrants).