`Ubaid bin Abi Qurrah said:

I heard Malik bin Anas say: `We raise whom We will in degrees` |al-An’am 6:83). He said: [i.e.] by means of knowledge. I said: Who told you that? He said. Zaid bin Aslam said that.

حَدَّثَنَا عُبَيْدُ بْنُ أَبِي قُرَّةَ، قَالَ سَمِعْتُ مَالِكَ بْنَ أَنَسٍ، يَقُولُ نَرْفَعُ دَرَجَاتٍ مَنْ نَشَاءُ قَالَ بِالْعِلْمِ قُلْتُ مَنْ حَدَّثَكَ قَالَ زَعَمَ ذَاكَ زَيْدُ بْنُ أَسْلَمَ‏.‏