Musnad Ahmad 482:148

Hassan narrated to us, Ibn Lahi'ah narrated to us, Abu 'Ashanah narrated to us, that he heard 'Uqbah ibn 'Amir narrating from the Messenger of Allah, peace and blessings of Allah be upon him, that he said: "When a man purifies himself, then comes to the mosque awaiting the prayer, his two scribes—or his scribe—record for him, for every step he takes toward the mosque, ten good deeds. And the one sitting awaiting the prayer is like the one standing in prayer (al-qanit), and he is recorded among those who pray from the moment he leaves his house until he returns to it."