The intelligence of this massacre {the St. Bartholomew's Day Massacre in 1572}(for which a solemn thanksgiving was offered up at Rome by order of the Pope) produced the same horror and consternation in Scotland as in every other Protestant country. It inflicted a deep wound on the exhausted spirit of Knox. Besides the blow struck at the whole Reformed body, he had to lament the loss of many individuals eminent for piety, learning, and rank, whom he numbered among his acquaintances. Being conveyed to the pulpit [in his old age], and summoning up the remainder of his strength, he thundered the vengeance of Heaven against that cruel murderer and false traitor, the King of France, and desired Le Croc, the French ambassador, to tell his master, that sentence was pronounced against him in Scotland, that the divine vengeance would never depart from him, nor from his house, if repentance did not ensue; but his name would remain an execration to posterity, and none proceeding from his loins would enjoy that kingdom in peace. The ambassador complained of the indignity offered to his master, and required the Regent to silence the preacher; but this was refused, upon which he left Scotland.
(From The Life of John Knox by McCrie)