The Prophet (may Allah’s peace and blessings be upon him) once spat into the palm of his hand, then placed his finger upon it and said:
“Allah said: O son of Adam, how can you think to overpower Me when I created you from something like this? And when I have fashioned you and formed you, you walk in your cloak on the earth and it groans beneath your tread.
You accumulate and do not spend until the death rattle reaches your throat, then you say, ‘I wish to give in charity’—but how could it be the time for charity?”

Narrated by Aḥmad (no. 17842) — and this is his wording —also narrated by Ibn Mājah (no. 2707), al-Ḥākim (no. 3855), and at-Ṭabarānī in al-Kabīr (no. 1194), from the narration of Busr ibn Jahhāsh al-Qurashī (may Allah be pleased with him).
Authenticated in Ṣaḥīḥ al-Jāmiʿ (no. 8144), and Silsilat al-ahādīth as-Ṣaḥīḥah (no. 1143).

Brief Explanation of the Hadith

Man is a weak and short-lived being — no matter how long his life extends, he has a fixed term and a set departure. Therefore, he should strive to fill his days with righteous deeds. Among the most hopeful and rewarding of these deeds is charity (ṣadaqah). For this reason, the Prophet (may Allah’s peace and blessings be upon him) was keen to instill this meaning in his Ummah — both through his words and his actions.
The Prophet (may Allah’s peace and blessings be upon him) was the most excellent of teachers, and among the hallmarks of his teaching was his use of parables and examples to make meanings more accessible to the mind. One such example is found in this hadīth: the Prophet (may Allah’s peace and blessings be upon him) spat into the palm of his hand—some of his saliva—then pointed to it with his finger to illustrate its insignificance and lowliness, thereby indicating that the human being, in origin, is as humble and insignificant as that saliva. The Prophet (may Allah’s peace and blessings be upon him) then said: “Allah, may He be exalted, said—addressing the son of Ādam: ‘How can you defy Me?’” This is a rhetorical question expressing rebuke, given the weakness and lowliness of the human condition. I created you and brought you into existence from a mere drop—something comparable in size, weakness, and insignificance to this small amount of spittle! So how can it befit you to show arrogance toward Me, or imagine that you can escape My power — that I am unable to hold you to account? Once your form was completed, and you stood upright and well-shaped, you walked in two fine garments, impressed with yourself. “And the earth echoed beneath your stride” — producing a sound beneath your heavy tread. You walked in pride, forgetting your origin and the lowly beginning from which you were created. And you forgot the blessings of Allah and His grace upon you. You busied yourself accumulating wealth and withholding due rights — until death drew near, and your soul reached the collarbones (tarāqī), rising to your throat. Then you said to yourself: “Shall I give in charity now?” But how could charity be accepted now, when its time has already passed and its opportunity has slipped away?
A confirmation of this meaning is found in the Book of Allah — may He be glorified and exalted — where He says: {Until, when death comes to one of them, he says, “My Lord, send me back so that I might do righteousness in that which I left behind!”} al-Mu’minūn: (99–100).
So, hasten toward good deeds and take initiative in performing righteous acts — for no soul knows when its appointed time will come.