The World Federation One Stop Fiqh

Ruling 1056

If a person cannot perform sajdah at all and the extent to which he can bend forward is not sufficient for it to be called sajdah, he must perform sajdah by indicating with his head. If he cannot do this, he must indicate with his eyes. If he cannot even indicate with his eyes, he must make the intention of performing sajdah in his heart; and based on obligatory precaution, he must indicate with his hands and suchlike and say the obligatory dhikr.