Ṣaḥīḥ Muslim Ḥadīth [1917]
It is narrated on the authority of Abī Hurayrah (may Allāh be pleased with him) that the Messenger of Allāh (peace and blessings of Allāh be upon him) said: “Be prompt in doing good deeds (before you are overtaken) by turbulence which would be like a part of the dark night. During (that stormy period) a man would be a Muslim in the morning and an unbeliever in the evening or he would be a believer in the evening and an unbeliever in the morning, and would sell his faith for worldly goods.”
Commentary by Shaykh ‘Abdul-‘Azīz ‘Alvī, Dārussalām, Maktabah Bayt-us-Salām, Shaykh al-‘Uthaymīn, and Ḥāfiẓ Ṣalāḥuddīn Yūsuf added.