It is narrated from Hazrat Anas (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: There are three things, whoever possesses them will taste the sweetness of faith: First, that Allah and His Messenger are more beloved to him than anyone else; second, that when he loves someone, he loves him only for the sake of Allah; and third, that after being saved from Judaism or Christianity, he dislikes returning to them just as he would dislike being thrown into the fire.
Hadith Referenceمسند احمد / مسند المكثرين من الصحابة / 14070
Hadith Gradingحکم دارالسلام:إسناده صحيح، خ: 16، م: 43، والمحفوظ فى حديث أنس فى "الصحيحين" و غيرهما: "أن يرجع فى الكفر" أو "يعود فى الكفر" انظر: 12783