One day the Holy Prophet (s) asked all the Muslims present: ‘According to Islam, which act of a believer denotes the strongest faith?’
‘Prayer,’ said one. ‘No,’ was the answer. ‘Zakaat,’ said another. ‘No,’ was the answer. ‘Fasting,’ proffered a third. ‘No’ was the answer. ‘Hajj,’ volunteered a fourth. ‘No,’ was the answer. ‘Jihad,’ said a fifth. ‘No,’ was the answer.
The Holy Prophet (s) then said, ‘All the things that you have mentioned are great and important essentials of faith, but not the answer to my question. The correct answer is: “Befriending for the pleasure of Allah and sundering relations for the approval of Allah.”
Reference : Anecdotes of The Ahlul Bayt (Daastaan e Raastaan ) by Ayatullah Murtadha Mutahhari