1538, Hugh Latimer, letter to Cromwell http://books.google.com/books?id=y5nVKvA2KoAC&pg=PA387&dq=accustomable+inauthor:Latimer&hl=en&ei=YvluTfjzN8iatwfw0pnFCg&sa=X&oi=book_result&ct=result&resnum=2&ved=0CC8Q6AEwAQ#v=onepage&q=accustomable%20inauthor%3ALatimer&f=false and the rest I commit to your accustomable goodness
Source: wiktionary