Hadith #2402 (Sunan al-Nasa'i)
Book: The Book of Fasting
Narrator(s): Abu al-Malih, Abu Qalaba, 'Abdullah bin Zayd al-Jarmi عبد الله بن زيد بن عمرو, Khalid bin 'Abdullah al-Tahan خالد بن عبد الله بن عبد الرحمن الطحان, Khalid bin Mahran al-Hadha' خالد بن مهران الحذاء, Wahb bin Bqyh bin 'Uthman وهب بن بقية بن عثمان, Zakaria bin Yahya bin 'Umar زكريا بن يحيى بن عمر

“The Messenger of Allah said: ‘I have heard that you stand (in prayer) all night and fast all day.’ I said: ‘O Messenger of Allah, I only meant good by that.’ He said: ‘One who fasts every day of his life has not truly fasted. But I will tell you what fasting for a lifetime means: Three days of every month.’ I said: ‘O Messenger of Allah, I said: ‘I am able to do more than that.’ He said ‘Observe the fast of Dawud, peace be upon him; he used to fast one day and not the next.”‘ ‘Ata said: “someone who heard him told me that Ibn ‘Umar (said) that the Prophet said: ‘Whoever fasts every day of his life, then he has not fasted.”

Source: https://parallelquran.com/hadith/sunan-al-nasai-2402/