Journal of PoF Twilight Sparkle 23041003CE:

There are times when I have found her in her room, leaning against her old Wonderbolts poster. I haven’t really found the courage to talk to her about it yet.. It just feels like one of those personal things… I know that she must have heard me walk in the few times I caught her, but she never says anything. I- *ink smudges a few lines* -f Celestia, I swear that I will find a way to help her fly again. I promise, Rainbow Dash, you will fly again. - Twilight Sparkle

Detailed version.

Journal of PoF Twilight Sparkle 23041003CE:

There are times when I have found her in her room, leaning against her old Wonderbolts poster. I haven’t really found the courage to talk to her about it yet.. It just feels like one of those personal things… I know that she must have heard me walk in the few times I caught her, but she never says anything. I- *ink smudges a few lines* -f Celestia, I swear that I will find a way to help her fly again. I promise, Rainbow Dash, you will fly again. - Twilight Sparkle