The advice of a father to his son “Beware of entrance to a quarrel, but being in, bear it that the opposed may beware of thee,” is good, and yet not the best. Quarrel not at all. No man resolved to make the most of himself can spare time for personal contention. Still less can he afford to take all the consequences, including the vitiating of his temper and loss of self control. Yield larger things to which you can show no more than equal right; and yield lesser ones, though clearly your own. Better give your path to a dog than be bitten by him in contesting for the right. Even killing the dog would not cure the bite.

Abraham Lincoln (1809-1865) American lawyer, politician, US President (1861-65)

Letter (1863-10-26) to J. M. Cutts
    (Source)

Never actually sent as a letter; likely conveyed in a personal reprimand interview with Cutts. The interesting story of Cutts' court-martial can be found here.