The Prayer of the One Who Cannot Prostrate

If you can stand up and perform ruku^, but cannot go down to the floor and prostrate, you do the following:
1. Face the Qiblah while standing
2. Say Allahu akbar with proper intention
3. Recite the Fatihah and a part of the Qur’an
4. Bend forward so that your palms reach your knees (ruku^) and remain there still as long as saying subhanallah takes (figure A1)
5. Straighten your back (i^tidal) and remain (standing) there still as long as saying subhanallah takes
6. Bend forward for prostration (sujud) lower than in step 4 (figure A2)

figure-A1 figure-A2

7. Straighten your back to the previous (standing) position
8. Repeat step 6 for a second prostration
9. Repeat step 7 to start the second rak^ah
10. Repeat steps 1-9. Raise your head
11. Sit in a seat for the tashahhud and what follow (figure A3). If you are praying the Fajr prayer, this is your last sitting and tashahhud until your salam (figure A4). When you pray the other obligatory prayers you add more rak^ahs

figure-A3 figure-A4

Another way to perform steps 5-10 is to sit on a seat (instead of standing up) and bend your back down with your head past your knees (figure A5) to perform prostration and other positions  (figure A4)