This happened during the last FIFA international window (break) for all national teams. It was a crucial Russia 2018 World Cup qualifier between Italy and Liechenstein. Italy were the visitors.
Reports say the match was so one-sided – i.e Italy dominated and pressurized them all through – that Buffon was on ‘holiday‘ and so a fan approached him for his autograph which he gladly obliged though with one eye on goings-on. on the pitch. Dunno if it is an offence and attracts a sanction…Crazy in’t?