I heard `Umar bin Al-Khattab saying, "I gave a horse to be ridden in Allah's Cause and the person who got it intended to sell it or neglected it. So, I wanted to buy it as I thought he would sell it cheap. I consulted the Prophet (ﷺ) who said, "Do not buy it even if for one Dirham, because he who takes back his gift is like a dog swallowing its vomit."
Sahih al-Bukhari Book 56, Hadith 212
← Previous Hadith `Umar bin Al-Khattab gave a horse to be ridden in Allah's Cause and then he found it being sold. He intended to purchase it. So, he consulted Allah's Messenger (ﷺ) who said, "Don't buy it and don't take back your gift of charity."

Sahih al-Bukhari Book 56, Hadith 211 Next Hadith → A man came to the Prophet (ﷺ) asking his permission to take part in Jihad. The Prophet (ﷺ) asked him, "Are your parents alive?" He replied in the affirmative. The Prophet (ﷺ) said to him, "Then exert yourself in their service."

Sahih al-Bukhari Book 56, Hadith 213