The Spain captain's error almost cost Real Madrid the Champions League on Saturday but his former team-mate insists his form earlier in the tournament was crucial
Diego Godin headed Atletico into the lead in Saturday's Champions League final after Casillas raced off his line and became stranded following a cross.
The goal looked set to hand Atletico the trophy until Sergio Ramos equalised in second-half injury time, before Madrid went on to win 4-1 after extra-time thanks to goals from Gareth Bale, Marcelo and Cristiano Ronaldo.
Raul - who played alongside Casillas for both club and country - says he is delighted to have seen Madrid finally win their 10th European title and insists the 33-year-old goalkeeper played a pivotal role throughout the competition.
"I feel happy, along with all Madridistas. Winning the European Cup - La Decima - is something historic, even more so as it comes after so much suffering and bad times," he said after the match.
"Iker had a great Champions League and a great season. It was unfortunate on the goal, but Madrid got to the final because he had many good days.
"He doesn't have to prove anything. I'm very happy for all of them and especially for him, as he got to lift the cup."