It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that once I saw the Prophet Muhammad (peace and blessings be upon him) with some pebbles in his hand, and he was cleaning the phlegm stuck towards the Qiblah with them, and he said: When any one of you is in prayer, he is conversing with Allah, so none of you should clean his nose in front of his face during his prayer.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 6306
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد حسن من أجل محمد بن إسحاق