Musannaf Ibn Abi Shayba 21:610

Ibn Fudayl narrated to us, from Wafa, from Sa’id ibn Jubayr, who said: Umar ibn al-Khattab saw a person performing tasbih (glorification) with [many] tasbihs. Umar, may Allah have mercy on him, said: "It suffices him of that to say: 'Subhan Allah' (Glory be to Allah) to the fullness of the heavens and the fullness of the earth and the fullness of whatever He wills of anything thereafter." And he said: "And he says: 'Allahu Akbar' (Allah is the Greatest) to the fullness of the heavens and the fullness of the earth and the fullness of whatever He wills of anything thereafter."