Sunan Ibn Majah
967
Daif+3

It was narrated from Ka’b bin ‘Ujrah that the Messenger of Allah (ﷺ) saw a man who had interlocked his fingers during the prayer, so the Messenger of Allah (ﷺ) separated his fingers

DaifAl-Albani
DaifMuhammad Fouad Abd al-Baqi