Sunan Abu Dawood, Chapter: Prayer (Kitab Al-Salat)

Abu Thumamah al-Hannat said that Ka'b ibn Ujrah met him while he was going to the mosque; one of the two (companions) met his companion (on his way to the mosque) And he met crossing the fingers of my both hands. He prohibited me to do so, and said: The Apostle of Allah (peace_be_upon_him) has said: If any of you performs ablution, and performs his ablution perfectly, and then goes out intending for the mosque, he should not cross the fingers of his hand because he is already in prayer.