What book is this quote from "we cannot tell the precise moment when friendship is formed. as in filling a vessel drop by drop, there is at last a drop which makes it run over; so in a series of kindnesses there is at last one which makes the heart run over." fahrenheit 451?

I agree with you, this quote is from the novel “Fahrenheit 451” by Ray Bradbury.

This particular quote is found on page 67, second paragraph of the novel “Fahrenheit 451” written by an American writer Ray Bradbury in 1953. This quote from Bradbury's “Fahrenheit 451” can be found also in “The Life of Samuel Johnson, LL.D.” written by James Boswell and it serves as an allusion because when Montag starts to read books he remembers his encounter with Faber, his lifelong friend, which is the same for Boswell and his lifelong friend Samuel Johnson.

renascimento comercial, que, a partir do século 11, inaugurou definitivamente a baixa idade média, que se estenderia até o século 15.