Musnad Abu Ya'la al-Mawsili 42:140

Ishaq narrated to us, Abd al-Samad narrated to us, Abd al-Hakam ibn Abd Allah al-Qass narrated to us, he said: Abu al-Siddiq al-Naji narrated to me, from Abu Sa’id, he said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Give glad tidings to those who walk in the darkness to the mosques of the complete light on the Day of Resurrection."