حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ سُفْيَانَ، حَدَّثَنَا مُحَمَّدُ بْنُ عُمَرَ بْنِ عَلِيِّ بْنِ أَبِي طَالِبٍ، عَنْ عَلِيٍّ
رَضِيَ اللَّهُ عَنْهُ قَالَ قُلْتُ: يَا رَسُولَ اللَّهِ إِذَا بَعَثْتَنِي أَكُونُ كَالسِّكَّةِ الْمُحْمَاةِ أَمْ الشَّاهِدُ يَرَى مَا لَا يَرَى الْغَائِبُ قَالَ الشَّاهِدُ يَرَى مَا لَا يَرَى الْغَائِبُ
I said: O Messenger of Allah (sallallahu alayhi wa sallam), when you send me on a mission, should I go and do what you tell me to do (with no delay) or witness and find out what someone who is not there cannot find out? He said: ‘Witness and find out what someone who is not there cannot find out.’.
Musnad Ahmad 593, Book 5, Musnad 'Ali Ibn Abi Talib, Hadith 65. 1 min read