How does shakespeare prove in his sonnet not times fool?

Shakespeare does not prove anything in Sonnet 116. Sonnets generally make an observation but do not attempt to "prove" it. Rather, he argues and persuades the addressee of the sonnet of love's enduring and unchanging nature using various devices to support his claim. Some literary and poetic devices employed may include imagery such as metaphors and comparisons, use of rhyme schemes, allusions, paradox, puns, enjambment, caesura, assonance, alliteration, anaphora, parallelism, irony, and contrast.