Al-Sa'ib bin Yazid related that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) saw Sayyiduna Zayd bin Khalid al-Juhani (may Allah be pleased with him) praying after Asr, so he struck him with his whip while he carried on praying as he was. When he finished, he said: "By Allah, O Commander of the Believers! I will never abandon it, since I have seen the Messenger of Allah (peace and blessings be upon him) offer this prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 5147