The Prophet ﷺ stood in prayer until his feet, or his shins, became swollen. It was said to him, "Messenger of Allah, has not Allah forgiven you your past and future sins?"He replied, "Should I not then be a grateful servant?"
قام النبي ﷺ حتى تورمت قدماه، ساقاه. قال: فقيل: يا رسول الله، قد غفر الله لك ما تقدم من ذنبك وما تأخر؟ قال: أفلا أكون عبدا شكورا.
Narrated by Abu Yaala (2900) from Abdullah bin Awn Kharraz, who said, Muhammad bin Bishr told us, from Misar bin Kidam, from Qatada, from Anas, and he related it. Haythami mentioned it in Majma (2/271) and attributed it to Abu Yaala, Bazzar, and Tabarani in Awsat, saying, "Its narrators are the narrators of sahih." I say, it is as he said, except that the hadith has been criticized on the grounds that the well-known version is from Misar, from Ziyad bin Alaqa, from Mughira bin Shuba, as mentioned earlier at the beginning of the chapter, and that is what Bukhari and Muslim recorded. However, it is not unlikely that this hadith has another source, namely what Muhammad bin Bishr related. He is al-Abdi, described as trustworthy and a hafiz, from Misar bin Kidam, from Qatada, from Anas, and he related it. Anas bin Malik was the servant of the Messenger of Allah ﷺ, and he observed things of the Prophet's ﷺ conduct that no one else observed.Supporting this route is what Abu Shaykh Asbahani related in Akhlaq an-Nabi ﷺ (p. 160), from Ahmad bin Muhammad bin Ali Khuzai, who said, Qurra bin Habib told us, who said, Abdul-Hakam told us, from Anas bin Malik, who said, "The Messenger of Allah ﷺ worshipped so much that he became like a worn-out waterskin. So they said, 'O Messenger of Allah, what drives you to this? Has Allah not already forgiven you your past and future sins?' He said, 'Should I not then be a grateful servant?'"However, this contains Abdul-Hakam, who is Ibn Abdullah Qasmali, daif as stated in Taqrib. Still, taken together, the two routes indicate that this hadith does have a basis going back to Anas as well.A point of benefit, Ibn Khuzayma said, "This shows that gratitude to Allah may be expressed through action performed for Him, since all gratitude belongs to Allah, and it may also be expressed through speech. Allah Most High says, "Work, O family of Dawud, in gratitude" [Saba 34:13], so He
commanded them to perform deeds of gratitude. Thus gratitude may consist of both speech and action together, not as commoners suppose, that gratitude is only expressed through the tongue."