“In the beginning and the end, it’s all a crapshoot. The Cosmic Mind does play dice. Loves to gamble, in fact.”

Source: The Born-Einstein Letters 1916-55

During the same 1994 exchange with Penrose as the previous quote, transcribed in The Nature of Space and Time (1996) by Stephen Hawking and Roger Penrose, p. 26 http://books.google.com/books?id=LstaQTXP65cC&lpg=PA26&dq=hawking%20%22where%20they%20can't%20be%20seen%22&pg=PA26#v=onepage&q=&f=false and also in "The Nature of Space and Time" (online text) http://arxiv.org/abs/hep-th/9409195
Unsourced variants: Not only does God play dice with the Universe; he sometimes casts them where they can't be seen.
Not only does God play dice, but... he sometimes throws them where they cannot be seen.
Variant: So Einstein was wrong when he said "God does not play dice". Consideration of black holes suggests, not only that God does play dice, but that He sometimes confuses us by throwing them where they can't be seen.

Imaginary Magnitude" (1981), "Lecture XLIII", tr. Marc E. Heine (1984)

"The Chances of Death" (1895)

[Gerolamo Cardano, Liber de ludo aleae, around 1560]

"In Search of a Majority: An Address" (Feb 1960); reprinted in Baldwin, "Nobody Knows My Name: More Notes of a Native Son" https://en.wikipedia.org/wiki/Nobody_Knows_My_Name (1961)

Conclusion
Elements of Physiology (1875)