Assalam o Alaykum !!
[Al-Bukhari; Kitab at-Tahajjud]
Comments:
If your friend gave you a beautiful sweater as a gift should you feel grateful to her in your heart? And if you feel grateful to her in your heart, shouldn’t you also use your tongue to show your appreciation of her favour? Gratitude doesn’t end here: Shouldn’t you then wear it on appropriate occasions? How would your friend feel if she saw you mopping the floor with her gift?
True gratitude (Shukr) involves the heart, tongue and limbs as it is the case of a complete Eeman which does not complete if not depicted by tongue, heart and limbs. That is why the Prophet (sal Allahu alaihi wa sallam) would stand up long during the night in prayer – to show with his limbs that he was grateful to Allah (subhana wa ta’ala) for his blessings on him.
Your Salah depicts your Eeman, as it has been termed as word ‘Eeman’ in Quran by Allah SWT.
Imagine this is the case of Rasool Allah sal Allahu alaihi wa sallam who is showing gratitude by performing Qayam ul Lail which is an optional Salah for his Ummah (for Him obligatory), that confirms gratitude, what about those who leave the Obligatory Salah (Farz)? Not only this can lead to nullify their Eeman but shows extreme ungratitude to Allah SWT.
Note: One who leaves Salah and take this as a habit can lead him/her to becoming an Apostate (Murtad) by the principles of Shariah. And some of the scholars with strong proofs from Quran and Sunnah are on that opinion that leaving only ONE Salah deliberately can make a Muslim turn to Kafir. Therefore, a Muslim shall be very careful about his/her Salah.