Is the reading of Ibn Masoud and Ibn Abbas (may Allah be pleased with them) for the verse: (And the sun runs on to its non-resting place) authentic, and are there other different readings in the verses of the Qur'an?

Summary of the answer: Some exegetes mentioned the reading (والشمس تجري لا مستقر لها) [the sun runs, having no resting place for it]. It was narrated with a chain of transmission by Abu Ubayd al-Qasim ibn Sallam, with a chain that includes Muhammad ibn Abi Hassan, who is unknown and might be Muhammad ibn Sa'id al-Shami, who was crucified for apostasy, which weakens the narration. Al-Qurtubi and al-Anbari invalidated this reading, emphasizing that the authentic narration from Ibn Abbas and Mujahid is (والشمس تجري لمستقر لها) [the sun runs to a resting place for it], and that this alleged reading contradicts scholarly consensus.

If this reading were authentic, it would allow for three possibilities: 1. It is a Qur'anic reading that is not mutawatir (mass-transmitted), but narrated by individual reporters. The preservation of the Qur'an is achieved by the survival of at least one of its authentic modes of recitation. 2. It is an explanatory reading, where some Companions would add words for clarification and explanation, not for transmission as part of the Qur'an. 3. It is an abrogated reading that the Companion was unaware had been abrogated. The Imam Mus'haf (the standard copy of the Qur'an) does not contain abrogated verses.