I am not responsible for any data loss or bricked devices! You do it on your own risk!
1) Download this zip. The password is: ccc333
2) Extract the zip to your desktop.
3) Download Android SDK Tools from here and install the packages.
4) Plug your Ascend P1 to the PC.
5) Make sure that USB Debugging is checked (Settings -> Developer options -> USB debugging)!
6) Open "b113_b115-root_u9200---__[Nixing]" from your desktop.
7) Run "hwadb.exe".
8) Run "ubl.exe", click ROOT - this should root your device without restart and any problem, check if the Superuser icon has appeared.
After the device is rooted you will need to install recovery.
I used Geno's Recovery - run "Onekey_ROM_Ascendp1.exe" from the zip and the tool will install it.
From this recovery you can flash whatever you want w/o any problems! It's a little bit sad that it is in chinese but oh well...
I will attach a picture of the same recovery but in english so you can see what you are actually doing.