Walaykum asalaam
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Sincerity towards Allah is the best type of sincerity. The Muslim is being sincere towards his Lord if he achieves sincerity in three aspects: faith and proper belief, acts of obedience, and morals and manners. Faith does not mean mere wishful thinking. The one who is sincere in his faith is the one who attains faith in the way his Lord wants from him, which includes sincerity in faith, sincerity in intention, and sincerity in fear of Allah, may He be exalted. Not every act of obedience is sincere unless it is done, both outwardly and inwardly, in a manner which Allah likes.
Allah has described the sincere in one verse, in which He says (interpretation of the meaning):
“It is not Al-Birr (piety, righteousness, and each and every act of obedience to Allaah) that you turn your faces towards east and (or) west (in prayers); but Al-Birr is (the quality of) the one who believes in Allaah, the Last Day, the Angels, the Book, the Prophets and gives his wealth, in spite of love for it, to the kinsfolk, to the orphans, and to Al-Masaakeen (the poor), and to the wayfarer, and to those who ask, and to set slaves free, performs As-Salaah (Iqaamat-as-Salaah), and gives the Zakât, and who fulfil their covenant when they make it, and who are patient in extreme poverty and ailment (disease) and at the time of fighting (during the battles).” Then Allah says, after listing all these attributes: “Such are the people of the truth and they are Al‑Muttaqoon (the pious)”
[al-Baqarah 2:177].
http://islamqa.info/en/126306