Ziyad bin Subaih Hanafi (may Allah have mercy on him) says that once I was praying next to Sayyiduna Ibn Umar (may Allah be pleased with them). I placed my hand on my waist. When he saw this, he struck my hand. When he finished his prayer, he said: Such severity in prayer? The Prophet (peace and blessings be upon him) used to forbid this.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 5836
Hadith Gradingحکم دارالسلام:صحيح لغيره، وهذا إسناد حسن.