ENOfficial
Abu Dharr said that God's messenger called him and laid a condition on him that he should not ask people for anything. When he agreed he said, "Not even for your whip when you drop it. You must dismount and get it yourself.” Ahmad transmitted it.
Source: sunnah.com
Other translations
Arabic
وَعَنْ أَبِي ذَرٍّ قَالَ: دَعَانِي رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَهُوَ يَشْتَرِطُ عَلَيَّ: «أَنْ لَا تَسْأَلَ النَّاسَ شَيْئًا» قُلْتُ: نَعَمْ. قَالَ: «وَلَا سَوْطَكَ إِنْ سَقَطَ مِنْكَ حَتَّى تنزل إِلَيْهِ فتأخذه» . رَوَاهُ أَحْمَدُ
sunnah.com