Hadith 8:25
Rafi' b. Khadij said God's Messenger was asked what type of earning was best and replied, “A man’s work with his hand and every business transaction which is approved.” Ahmad transmitted it.
وَعَنْ رَافِعِ بْنِ خَدِيجٍ قَالَ: قِيلَ: يَا رَسُولَ اللَّهِ أَيُّ الْكَسْبِ أَطْيَبُ؟ قَالَ: «عَمَلُ الرَّجُلِ بِيَدِهِ وَكُلُّ بَيْعٍ مَبْرُورٍ» . رَوَاهُ أَحْمَدُ
Original Reference: Mishkat al-Masabih 2783