Musnad Ahmad Hadith 4849

Ziyad bin Subaih Hanafi (may Allah have mercy on him) says that once I was standing in front of the Ka'bah offering prayer, and an elderly man was sitting beside me. I prolonged my prayer and at one point placed my hand on my side. When the mentioned Sheikh saw this, he struck my chest in such a way that he left no leniency. I thought to myself, what problem does he have with me? So I quickly completed my prayer. I saw that a slave was sitting behind him. I asked, who is this elder? He told me that this is Abdullah bin Umar (may Allah be pleased with them both). I sat down until he finished his prayer. I said to him, O Abdur Rahman! What problem did you have with me? He asked, was that you? I replied, yes! He said, such severity in prayer? The Prophet (ﷺ) forbade this.