Mourinho said: "Wayne is and has been England's best player for over a decade and this game will be a fitting tribute to everything he has achieved.
ACE 16.1 Primeknit Sliver UK "I'm looking forward to what will be a very special night for us both.
"I'm sure the fans will make this a memorable occasion and help Wayne to raise a lot of money to help support vulnerable children."
FootballX black Having come through the youth ranks at Everton and made a major impression in the first team, Rooney left to join United in 2004.
hypervenom Ousadia Alegria He has gone on to score 245 goals for United, putting him only four behind Sir Bobby Charlton's all-time record haul for the club, and helped them secure plenty of silverware, including five Premier League titles and the 2007-08 Champions League.
Rooney has expressed his gratitude to Everton and United for what they have done for him and emphasised he will "never play for another Premier League club" - something that would appear not to rule out a return to the Goodison Park outfit in the future.
Profiles Wayne Rooney
"For me there could not be a more special testimonial match," the England skipper said on Thursday.
"Manchester United and Everton are the only clubs I have played for as a professional footballer. I am happy to say now that, whatever may happen in the future, I will never play for another Premier League club.
"I owe United and Everton everything for giving me my footballing opportunities."
Rooney briefly wore an Everton shirt again last August when he played in Duncan Ferguson's testimonial at Goodison Park.
Everton chairman Bill Kenwright said of Rooney in Thursday's announcement: "I couldn't be more proud today of the young man who I first saw as an extraordinary 13-year-old.
"I was thrilled for him last August when Goodison Park showed him its admiration as he ran on to the pitch for his first hero, Duncan Ferguson's testimonial.
"Subsequently, it was one of the easiest decisions we have ever made at Everton in agreeing to support Wayne Rooney's testimonial by playing Manchester United at Old Trafford this August.
"We will try to win, Wayne, I promise you - but we will nonetheless be saluting one of our own who has gone on to become one of sport's great icons and who still retains all of the genius, passion and love for the game that was there when he was 13."
The Old Trafford match kicks off a year of fundraising events by the Wayne Rooney Foundation aimed at raising £5million for disadvantaged and vulnerable children
All proceeds from the game and all other events will be distributed through the foundation to four charities - the NSPCC, Claire House Children's Hospice, Alder Hey Children's Hospital and the Manchester United Foundation.
Rooney added: "Through the Wayne Rooney Foundation I want to put something back and, at the same time, say a heartfelt thanks to everyone at these great clubs who ever helped me in my career.
Superfly CR7 324K "Everton and United, along with my family, gave me the support and opportunity to help me achieve my goals and dreams.
"Having a young family of my own makes me realise it's vital that every child gets the opportunity to grow up surrounded by love and support to give them a chance of fulfilling their potential.
Tiempo Legend 6 black "I hope The Wayne Rooney Foundation and its charity partners can improve and inspire the lives of children disadvantaged by family breakdown, abuse, health issues or lack of educational opportunities."
