It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with them both) that the Noble Prophet (peace and blessings be upon him) heard a man advising another regarding modesty (saying: do not be so modest), so the Noble Prophet (peace and blessings be upon him) said: "Modesty is a part of faith."
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 4554