‘A’ishah, may Allah be pleased with her, reported:
When Allah’s Messenger [SAWS] occupied himself in the prayer at night, he observed it with such a extended qiyam (posture of standing) until his feet were swollen.
‘A’ishah said: “Allah’s Messenger, you do this in spite of the fact that your earlier and latter sins have been forgiven for you?”
He [SAWS] replied: “‘A’ishah, should I not prove myself to be a thankful servant of Allah?”
One of the lessons that we derive from this hadith is that shukr is by action. The Prophet [SAWS] stood up in prayer to show his thankfulness (shukr) to Allah [SWT]. He did an action (the prayer) to show his gratitude towards Allah.
Being thankful to Allah is not easy. It’s very easy to be heedless (ghafil), but very hard to be thankful. A dua to help us be thankful is:
Transliteration (hover your mouse for translation)
Allahumma a’inni ‘ala dhikrika
wa husni `ibadatika,
“O Allah, help me to remember You, to thank You, and to worship You in the best way.”
May Allah [SWT] give us the tawfeeq to do actions to thank Him, and to not just talk. Ameen.
P.S. The afore-mentioned du’a is recommended either during prayer before making the exiting salam, or immediately after prayer.