It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: Removing the hair below the navel, cutting the nails, and trimming the mustache are part of natural disposition (fitrah).
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 5988
Hadith Gradingحکم دارالسلام:إسناده صحيح ، خ: 5890.