Saul told the soldiers who were going to fight Goliath, that Allah will test them. They get to a river and they should not drink water from it. Only those who resist drinking from the river will stay with him, but those who drink are not with him, unless they only fill their cupped hand only and drink from it. Most of the warriors drank so they did not continue the journey with Saul.
(When Saul marched forth with his army, he cautioned: “Allah will test you with a river. So whoever drinks ˹his fill˺ from it is not with me, and whoever does not taste it—except a sip from the hollow of his hands—is definitely with me.” They all drank ˹their fill˺ except for a few! ) Al-Baqara 2:249
قال لهم طلوت أن الله سيمتحنهم عندما يصلوا إلى النهر. أنهم عليهم أن لا يشربوا من النهر. و من يشرب من النهر فلن يكون مع جنود طالوت. إلا إذا اغترف بيده الماء القليل و شربه فلا بأس. و أكثر الجنود شربوا من النهر و لم يستمروا الرحلة مع طالوت.
فَلَمَّا فَصَلَ طَالُوتُ بِالْجُنُودِ قَالَ إِنَّ اللَّـهَ مُبْتَلِيكُم بِنَهَرٍ فَمَن شَرِبَ مِنْهُ فَلَيْسَ مِنِّي وَمَن لَّمْ يَطْعَمْهُ فَإِنَّهُ مِنِّي إِلَّا مَنِ اغْتَرَفَ غُرْفَةً بِيَدِهِ ۚ فَشَرِبُوا مِنْهُ إِلَّا قَلِيلًا مِّنْهُمْ ۚ فَلَمَّا جَاوَزَهُ هُوَ وَالَّذِينَ آمَنُوا مَعَهُ قَالُوا لَا طَاقَةَ لَنَا الْيَوْمَ بِجَالُوتَ وَجُنُودِهِ ۚ قَالَ الَّذِينَ يَظُنُّونَ أَنَّهُم مُّلَاقُو اللَّـهِ كَم مِّن فِئَةٍ قَلِيلَةٍ غَلَبَتْ فِئَةً كَثِيرَةً بِإِذْنِ اللَّـهِ ۗ وَاللَّـهُ مَعَ الصَّابِرِينَ ﴿٢٤٩ ) البقرة 2: 249