Tafsir of Az-Zukhruf 43:56

{فَجَعَلْنَاهُمْ سَلَفًا}: Ibn Abbas, Zayd ibn Aslam, and Qatadah said: i.e., those who preceded [the others] into the Fire.

Many others have said: An example for the disbelievers who come after them, as they follow them in meriting the same punishment that descended upon them. The speech is metaphorical, for the successor follows the predecessor; so when they followed them in disbelief, it was as if they had followed them into the causal effect of [God’s] wrath. It [the word salaf] is an infinitive used as a descriptor, which is why it is valid to apply it to both the few and the many. It is also said: It is the plural of salif, like haris (guard) and haras (guards), or khadim (servant) and khadam (servants). This could mean the plural in its literal sense, or it could be a collective noun, for fa‘al is not a common pattern for plurals due to its prevalence in singular nouns. The famous plural for it is aslaf, and sulaf has also been used.

Abu Abdullah and his companions, Sa’id ibn ‘Ayyad, al-A’mash, al-A’raj, Talhah, Hamzah, and al-Kisa’i read it as {sulufan} (with two dammahs), the plural of salif, similar to fariq in both pronunciation and meaning. Al-Qasim ibn Ma’n heard the Arabs say: "A suluf of people has passed," meaning a group of them. It is also said to be the plural of salaf, like subr being the plural of sabir, or like junub.

‘Ali (may God ennoble his countenance), Mujahid, and al-A’raj also read it as {salafan} (with a fatha). This is either because the dammah of the lam was changed to a fatha for ease of pronunciation—as one says jadad with a fatha instead of judud with a dammah—or it is the plural of salfah, meaning a nation or group of people; i.e., "We made them a nation that has passed." Salaf (with a dammah followed by a fatha, in contexts other than this) refers to the offspring of a partridge, and its plural is salfan like surdan.

{وَمَثَلًا لِلْآخِرِينَ}

i.e., a lesson for them. The ones meant are the disbelievers who come after them. The prepositional phrase is connected to both salafan and mathalan due to the dispute between them [in governance]. It is also permissible that by mathal (example/proverb), it is meant an astonishing story that travels as proverbs travel. The meaning of their being a mathal for the disbelievers is that it is said to them: "Your likeness is the likeness of the people of Pharaoh." It is also possible that the prepositional phrase attaches to the second noun, and that the term al-akhirin (the later ones) is generalized to include the believers as well, as them being an astonishing story for all is clear.