It is narrated from Abu Uthman al-Nahdi that Sayyiduna Abu Hurairah (may Allah be pleased with him) was on a journey. He stopped at a place and sent a messenger to him while he was praying, so that he could come and eat. He said to the messenger: I am fasting. When the food was served and it was near that they would finish, he also started eating. Then he looked towards his messenger, so he said: He had told me that he was fasting. Sayyiduna Abu Hurairah (may Allah be pleased with him) said: He spoke the truth. I heard the Messenger of Allah (peace and blessings be upon him) say: "Fasting in the month of patience and fasting three days of every month is equivalent to fasting forever." I have already fasted three days of the month. I am one who leaves fasting in Allah’s concession and fasts in Allah’s strengthening.
Hadith Referenceمسند اسحاق بن راهويه / كتاب الصوم / 396
Hadith Takhrij«مسند احمد : 384/2 . 513 . صحيح ابن حبان ، رقم : 3659 . قال شعيب الارناوط : اسناده صحيح»
Abu Uthman al-Nahdi narrated: I hosted Sayyiduna Abu Hurairah (may Allah be pleased with him) for seven days; with him were his wife and his servant. They had assigned turns for the third parts of the night: one would stand (in prayer) while the other slept, and when this one stood, the other would sleep. And I heard Sayyiduna Abu Hurairah (may Allah be pleased with him) say: The Messenger of Allah (peace and blessings be upon him) distributed dates, and my share was seven dates. Among them was one spoiled, dry date, and it was the most beloved to me; it made my chewing of the dates stronger. Sulaiman said: That is, it had strength. The narrator said: I asked, "Abu Hurairah! How do you fast in the month?" He replied: "I fast three days at the beginning of the month, so if any issue arises for me, I have the reward for the whole month."
Hadith Referenceمسند اسحاق بن راهويه / كتاب الصوم / 397
Hadith Takhrij«بخاري ، كتاب الاطعمة ، باب الحشف : 5441 . مسند احمد : 353/2 . ارواء الغليل : 100/4»