The Holy Prophet of Islam (peace be upon him and his progeny) said:
"لاَ تَنْظُرُوا إلى كَثْرةِ صَلاتِهِمْ و صَوْمِهِمْ وَ كَثْرَةِ الْحَجِّ و الْمَعْرُوفِ و طَنْطَنَتِهمْ بِالليْلِ وَلكِنْ اُنْظُرُوا إلى صِدْق الْحَدِيْثِ وَ أَداءِ الأَمانَةِ"
Do not respect only the excessives prayer, fasting, pilgrimage, righteousness with others and vigil of some people (although they are important in their own right). Rather, consider their “honesty” and “trustworthiness”!1
A quick study of Islam clearly establishes the fact that the two decisive signs of a real Muslim are that he is honest and trustworthy. Performance of prayers, fasting and pilgrimage are certainly important and carry a high educational value but they are not a conclusive proof of a true Muslim. To complete the picture, a true Muslim must possess honesty and trustworthiness.