The young Dirichlet had … an old, worn copy of the Disquisitiones Arithmeticae of Gauss.

The story was told that the young Dirichlet had as a constant companion all his travels, like a devout man with his prayer book, an old, worn copy of the Disquisitiones Arithmeticae of Gauss.

— Heinrich Tietze (Austrian mathematician, 1880 – 1964)