Then when Saul set out with the army, he said: "Verily! Allah will try you by a river. So whoever drinks thereof he is not of me, and whoever tastes it not, he is of me, except him who takes (thereof) in the hollow of his hand."
Yet, they drank thereof all, except a few of them. So when he had crossed it (the river), he and those who believed with him, they said: "We have no power this day against Goliath and his hosts."
But those who knew with certainty that they were to meet their Lord, said: "How often a small group overcame a mighty host by Allah's Leave?" And Allah is with the patient.
And when they advanced to meet Goiath and his forces, they invoked: "Our Lord! Pour forth on us patience and make us victorious over the disbelieving people." Surah 2: 249-250
Related Quran Ayaaths of this Hadith.
"When a person dies, his works end, except for three: ongoing charity, knowledge that is benefited from, and a righteous child who prays for him."
Prophet Mohammed (PBUH)
"The best of what a man leaves behind are three: a righteous child who supplicates for him, ongoing charity the reward of which reaches him, and knowledge that is acted upon after him."
Sunan Ibn Mājah
"Every day two angels come down from Heaven and one of them says, 'O Allah! Compensate every person who spends in Your Cause,' and the other (angel) says, 'O Allah! Destroy every miser.'"
Sahih Bukhari