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It would have been difficult for Yamamoto Kantoku to specifically say that, since Hiroshima and Nagasaki bombings did not occur until after his own death and way after Pearl Harbor.

While Yamamoto may not have known the means, I’m sure he realized that in the end, it would be ugly for Japan.

He had also spent years in the United States and Britain as part of the delegations at the Washington and London Naval Talks. These years had given him a firsthand look at American industrial might and moral character, and was convinced to the very center of his being that the only way to possibly win the war he was ordered to prosecute was by a gamble.

An all-out air raid on the American naval headquarters in the Pacific, Pearl Harbor. Win in the first 24 hours, then negotiate a settlement favorable to Japan while the US was weak. At this, even, he was dubious. Asked by the Crown Prince to assess the odds of winning the war, he replied, "If necessary, I can run wild for the first six months. Beyond that I have no hope."

As the success of the Pearl Harbor Raid became clear on December 7th, 1941, his staff congratulated him. Yamamoto was on the Combined Fleet flagship, the battleship Nagato, sitting silently with eyes closed along the wall. He rose and said, "I fear all we have done is to awaken a sleeping giant and fill him with a terrible resolve." Then he excused himself and walked out on to the deck of the Nagato, where he stared out at the sea.

Source.

So sorry. Nothing from the archives of the Japanese Imperial Navy. The bold section is widely quoted, but may be fictitious.