The Turkey international has fond memories of his time at Real Madrid, and has praised his former coach's honesty
The midfielder left BVB for Madrid in the summer of 2011, but failed to secure regular first team action under Mourinho.
He returned to Dortmund on an 18-month loan deal this winter after an unsuccessful loan spell at Liverpool in the first-half of the season, yet he has fond memories of his time with Mourinho.
"It was an honour to work with Mourinho. He was always honest to me and treated me fairly. He always said everything to me in private," Sahin was quoted as saying by Sport Bild.
"From the outside, people will perhaps say that I failed abroad. It was simply not meant to be, though, and I also played my part in it."
Sahin has made eight Bundesliga appearances since his return to BVB, scoring two goals in the process.