At 17:19 of the second period in the Capitals/Penguins game, Washington requested a Coach's Challenge to review whether a Pittsburgh player interfered with Washington goaltender Philipp Grubauer prior to Evgeni Malkin's goal.
After reviewing all available replays and consulting with NHL Hockey Operations staff, the Referee confirmed that the actions of Washington's Daniel Winnik caused Pittsburgh's Patric Hornqvist to contact Grubauer before the puck crossed the goal line. The decision was made in accordance with Note 2 of Rule 78.7 (ii) which states, in part, that the goal on the ice should be allowed because "the attacking Player was pushed, shoved or fouled by a defending Player causing the attacking Player to come into contact with the goalkeeper."
Therefore the original call stands - good goal Pittsburgh Penguins.
Since the Coach's Challenge did not result in the original call being overturned, the Washington Capitals forfeit their time-out.