It's from Mencius. Check here:
http://books.google.com/books?id=_CdIAA ... &ct=result
It's also found in
The Works of Mencius, ch. 8
'This is illustrated in the passage of the T'âi Chiâ, "When Heaven sends down calamities, it is still possible to escape them. When we occasion the calamities ourselves, it is not possible any longer to live."'
http://nothingistic.org/library/mencius/mencius13.html