The BSE Sensex declined by 124 points to 19,635 in afternoon trade after paring initial gains of the opening session today. Earlier, the 30-share index rose by nearly 100 points on the back of strong rally in Infosys as market cheered N R Narayana Murthy's return as the company's executive chairman.Similarly, the National Stock Exchange Nifty was down 41 points, to trade at 5,944.