Многие путают.
Речь идет не о фильме, в котором (и в сценарии, и в оригинальной версии, и в переводе на русский) действительно есть эта фраза.
Речь о романе Пьюзо

вот нашел в романе Пьюзо:

Thinking this made him feel guilty about not feeling more sympathy for his father. His own father shot fall of holes and yet in a curious way Michael, better than anyone else, understood when Tom had said it was just business, not personal. That his father had paid for the power he had wielded all his life, the respect he had extorted from all those around him.

Book 1. Chapter 9

вот еще нашел в романе Пьюзо, немного перефразированно, но все же:

“You, the high class college kid, you never wanted to get mixed up in the Family business. Now you wanta kill a police captain and the Turk just because you got your face smashed by McCluskey. You’re taking it personal, it’s just business and you’re taking it personal. You wanta kill these two guys just because you got slapped in the face. It was all a lot of crap. All these years it was just a lot of crap.”

Book 1. Chapter 10

продолжаем )) :

With the old man gone, the Family power is cut at least in half. I would be fighting for my life anyway to keep all the businesses the old man got together. Drugs are the coming thing, we should get into it. And his knocking off the old man is purely business, nothing personal

Book 1. Chapter 4

вот еще:

‘That’s a waste.’ Sure, we’re not going to let anybody stop us if the old man says we go after Sollozzo. But this is not a personal thing, this is business. If we go after the Turk and the Families interfere, we’ll negotiate the issue. If the Families see that we’re determined to have Sollozzo, they’ll let us. The Don will make concessions in other areas to square things. But don’t go blood crazy on a thing like this. It’s business. Even the shooting of your father was business, not personal. You should know that by now.”

Book 1. Chapter 8

столько много:

You shouldn’t let that broken jaw influence you,” Hagen said. “McCluskey is a stupid man and it was business, not personal.”

ok 1. Chapter 11

извини, что заспамил )))

Значит, у меня неправильный роман Пьюзо )
http://pro-kuratora.livejournal.com/738056.html?thread=1769736#t1769736
Можно было в одном комментарии, да

почему не правильный... может там есть и та фраза, которую ты написал... но хотелось бы ее увидеть в оригинале, чтобы сравнить с той, где я искал