Musannaf Ibn Abi Shayba 21:606

Shababa narrated to us, from Shu'bah, from Abu al-Tayyah, from Murriq al-Ijli, from Ubayd ibn Umayr, who said: If you are unable to endure the night (in prayer), and unable to struggle against the enemy, and unable to spend wealth, then increase in saying: "Subhan Allah" (Glory be to Allah), "Alhamdulillah" (Praise be to Allah), "La ilaha illallah" (There is no god but Allah), and "Allahu Akbar" (Allah is the Greatest). For they are more beloved to me than two mountains of gold and silver.