Musnad Abu Ya'la al-Mawsili 110:230

Zuhayr narrated to us, Yunus bin Muhammad narrated to us, Layth narrated to us, from Qays bin al-Hajjaj, from Hanash al-San'ani, from Abdullah bin Abbas, that he narrated: That he rode behind the Prophet, may Allah bless him and grant him peace, one day. The Messenger of Allah, may Allah bless him and grant him peace, said to him: "O young boy, I will teach you some words: Guard Allah, and He will guard you. Guard Allah, and you will find Him before you. If you ask, ask Allah; and if you seek help, seek help from Allah. And know that if the nation were to gather together to benefit you with something, they would not benefit you except with something that Allah has already written for you. And if they were to gather together to harm you with something, they would not harm you except with something that Allah has written against you. The pens have been lifted, and the scrolls have dried."