The Meaning of the Hadith: "One-third is a lot" and Its Reason

Question:
He says: A hadith was reported, O Shaykh, in which the Messenger (peace and blessings be upon him) said, "One-third, and one-third is a lot." What is the occasion for this and what is its meaning?

Answer:
The occasion or reason for this is that Sa'd ibn Abi Waqqas (may Allah be pleased with him) fell ill with a severe illness, so the Prophet (peace and blessings be upon him) came to visit him in his sickness. Sa'd said, "O Messenger of Allah, indeed ?" He said, "No." He said, "Then half of it, a portion of it?" He said, "No." He said, "Then one-third of it?" He said, "Yes, one-third, and . Yes."