The Englishman is subject of transfer speculation, with Manchester United having the most serious interest.
However, Dortmund wanted 120 million euros and set a deadline for a deal to be completed by Monday this week.
But that date has passed and the club says Sancho will be staying for at least another season.
And that has pleased veteran defender Hummels a great deal.
"He can be the player who makes the difference," the German defender told reporters.
"I'm happy that he stays."