Qur'aan

The Holy Qur'aan warns against Hypocrites in Sura 63 Munafiqoon Verse 4

When you see them, their exteriors (outer trappings) please you; and when they speak, you listen to their words. They are as (worthless as hollow) pieces of timber propped up, (unable to stand on their own). They think that every cry is against them. They are the enemies; so beware of them. The curse of Allah be on them! How are they deluded (away from the Truth)!

Hadith

It is reported in Mishkat from Hazrat Abu Said Khudri (Radiallhu Anhu) who narrates that: "Once we were in the presence and company of the Holy Prophet (sallallahu alai hi wa sallam). He was distributing the booty (Spoils of War) when a person named Zul-Khawaisara, who was from the tribe of Bani Tamim addressed the Holy Prophet (sallallahu alai hi wa sallam) "Oh Muhammad Be Just!" ". The Prophet (Sallal Laahu Alaihi Wasallam) replied: "A Great pity that you have doubts, if I am unjust then who will be just, you are a loser and a failure." Zul-Khawaisara's attitude infuriated Hazrat Umar (Radiallhu Anhu) and he pleaded with the Prophet (sallallahu alai hi wa sallam)to permit him to slay Zul-Khawaisara. The Prophet (sallallahu alai hi wa sallam) remarked: "Leave him, as his slaying will serve no good purpose, as he is not the only individual but there are a host of others like him and if you compare their prayers and fasting to that of yours, you yourself will feel ashamed. These are the people who will recite the Quran but it will not go beyond their throats, with all these apparent virtues they will leave the fold of Deen just like the arrow leaves the bow. 

Miskhat Shareef, pp/535 / Alim-CD-Rom  Bukhari Shareef 9:527 & 8:184

Sufi Wisdom

Imam Malik says

 Whoever has the outer Law  (shariah) without the inner Reality (Sufism) has left the right way;

Whoever has the inner Reality (Sufism)  without the outer Law  (shariah) has strayed;

Whoever joins the two of them has realization.