He said it in a question and answer session in Kazakhstan 1st July 2013, look it up yourself.Your use of the phrase EU expansion is incorrect. It is not the EU expanding and gobbling up other countries, it is those other countries applying for membership of the EU, of their own free will, and going through the process of meeting all the required criteria.
The EU requires strict compliance with its requirements before other countries are allowed to join, and then provisional restrictions may applied for a limited amount of time. SO the EU is intentionally making it difficult for other countries to join.
The UK is a strong advocate of making it mote difficult. The UK's voice will be lost when we leave.
When did David Cameron say he would like to see the EU expand into the Ural Mountains?
He claimed that the British people supported further expansion into former Russian territories.
He also thought that allowing Ukraine into the EU would be a good idea.