Musnad Ahmad 26:429

Yahya ibn Adam narrated to us, Sharik narrated to us, Ali ibn al-Aqmar narrated to us, from Abu al-Ahwas, from Abdullah, who said: "We have seen ourselves, and the prayer would not be established until the rows were completed by us. So whoever is pleased to meet Allah, the Almighty and Majestic, tomorrow as a Muslim, let him maintain these prescribed prayers where they are called out. For they are among the paths of guidance, and Allah, the Almighty and Majestic, has legislated for your Prophet, may Allah bless him and grant him peace, the paths of guidance."