كتاب الوصايا
Read the English translation first, with the original Arabic directly underneath.
It was narrated that Abu Hurairah said:
"A man came to the Prophet (ﷺ) and said: 'O Messenger of Allah, what kind of charity brings the greatest reward?' He said: 'To give in charity when you are healthy and feeling miserly, and fearing poverty and hoping for a long life. Do not wait until the (death rattle) reaches the throat and then say: "This is for so and so," and it nearly became the property of so and so (the heirs).'"
أَنْ تَصَدَّقَ وَأَنْتَ صَحِيحٌ شَحِيحٌ تَخْشَى الْفَقْرَ وَتَأْمُلُ الْبَقَاءَ وَلاَ تُمْهِلْ حَتَّى إِذَا بَلَغَتِ الْحُلْقُومَ قُلْتَ لِفُلاَنٍ كَذَا وَقَدْ كَانَ لِفُلاَنٍ