“We set out until we came to the
Messenger of
Allah (ﷺ), and we gave him our oath of allegiance and
performed
prayer behind him. He glanced out of the corner of his eye
at a man
who was not settling his spine when he bowed and prostrated.
When the
Prophet (ﷺ) finished the prayer, he said: ‘O Muslims, there
is no
prayer for the one who does not settle his spine when bowing and
prostrating.’”
Sunan Ibn Majah Book 5, Hadith 69