وَلَمَّا وَرَدَ مَاءَ مَدْيَنَ وَجَدَ عَلَيْهِ أُمَّةً مِّنَ النَّاسِ يَسْقُونَ
فَسَقَىٰ لَهُمَا (So he (Musa) watered (their animal) for their sake - 28:24). That is Sayyidna Musa (علیہ السلام) took pity on the girls and drew out 'water from the well and satiated their goats. It is reported in some narrations that the shepherds after making their cattle drink water used to place a very heavy stone on the mouth of the well to make it unusable, and hence these girls would have only the left over water for their herd. The stone was so heavy that ten men together could move it, but Sayyidna Musa (علیہ السلام) removed it all by himself, and drew water from the well. Perhaps for this reason one of the two girls reported to her father that Sayyidna Musa was very strong. (Qurtubi)
ثُمَّ تَوَلَّىٰ إِلَى الظِّلِّ فَقَالَ رَبِّ إِنِّي لِمَا أَنزَلْتَ إِلَيَّ مِنْ خَيْرٍ فَقِيرٌ (Then he turned to a shade and said, "0 my Lord, I am in need of whatever good you send down to me." - 28:24). Sayyidna Musa (علیہ السلام) did not have any food for the last seven days. He came under the shade of a tree and prayed to Allah describing his condition and need in an exquisite manner. The word Khair is sometimes used for wealth as in the case of إِن تَرَكَ خَيْرًا الْوَصِيَّةُ (he leaves some wealth - 2:180). Sometimes it is used for strength like أَهُمْ خَيْرٌ أَمْ قَوْمُ تُبَّعٍ they better, or the people of Tubba - 44:37) and sometimes for food as in the verse under reference. (Qurtubi)