The Salaf about Hypocrisy

Al-Bukhari reported and commented that Ibn Abi Malika said, ‘I have caught up with 30 of the companions of the Prophet, salah allahu ‘alayhi wa salam, each fearing hypocrisy for themselves’.

When Abu Al-Darda used to finish Al-Tashahud in his salat, he used to always seek refuge in Allah from Hypocrisy. So he was asked, ‘What do you have to do with hypocrisy?’. Abu Al-Darda replied, ‘A person might have religion stripped with an hour his heart changes’ [Al-Thahabi says 'Saheeh' in his Siyar, 6/382]

Ahmad bin Hanbal was asked, ‘What do you say about a person who does not fear hypocrisy for himself? He replied, ‘And who does not fear hypocrisy for himself?’ [Jami' Al-Uloom wal Hikam, Ibn Rajab, 2/493]

Al-Hasan Al-Basri said, ‘Nobody feared it [hypocrisy] except a believer, and nobody felt safe of it except a hypocrite’ [Al-Khalal in Al-Sunnah, 5/68]