The word(s) "weaken" appears 2 time(s) in 2 verse(s) in Quran in Muhammad Pickthal translation.

(1) And with how many a prophet have there been a number of devoted men who fought (beside him). They quailed not for aught that befell them in the way of Allah, nor did they weaken, nor were they brought low. Allah loveth the steadfast.

(2) Then look again and yet again, thy sight will return unto thee weakened and made dim.