China Citic Bank, the country's seventh-largest lender by assets, plans to sell a five percent stake to the UK bank Barclays, ahead of a two billion US dollars initial public offering in Hong Kong, the South China Morning Post reported, citing sources.   Barclays, the third-largest British bank by market value, will be buying into a mainland bank for the first time, the report said. CITIC Bank is China's seventh-largest lender by assets.   CITIC Bank's parent, conglomerate CITIC Group, has said it is looking for a single foreign investor to take a 5% to 10% stake in the mid-sized lender before its initial public offering, said the paper.