Those who used to say: if he has not stood fully, no prostration of forgetfulness is due on him

Al-Aswad and Alqamah would sometimes, when rising from prostration (instead of sitting for the tashahhud), mistakenly rise so far that their buttocks were raised, but then they would sit down, and they did not perform the prostrations of forgetfulness.

Ibrahim said: Alqamah led the prayer; after two rak'ahs he began to rise, but before he had stood up fully the people said "Subhan Allah", and he sat down. And for this lapse he did not perform the two prostrations of forgetfulness.

Al-Dahhak said, concerning one who begins to stand up after two rak'ahs: If he remembers while he is still bent over (not yet fully standing), he should sit down.

Al-Zuhri said, concerning a man who makes a lapse in the prayer: If he has stood up straight, the two prostrations are required of him; and if he remembers before standing up fully, the prostration of forgetfulness is not required of him.