Salam, what is meant with "Mula'anah" in sura 29,46 tafsir Ibn Abbas.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Verse 46 of Surat Al-ankaboot (The Spider) has nothing to do with Li’aan. Rather, it includes the command to the believers to argue with Ahl Al-kitab (People of the Book) in the best way, and not to be harsh with them, except for those who are obstinate. The verse that is mentioned informs the believers that if the People of the Book talked to them about their books, with what they can be truthful, or they may be liars, and they [beleivers] did not know their situation about that, to tell them {We believe in that which has been revealed to us and revealed to you}; i.e, in what was revealed in the Torah and the Bible, {And our God and your God is one} which means: the One Whom we worship and the One Whom you is one, {and we are Muslims [in submission] to Him}; which means: Submissive and humiliated with obedience to what Allah commanded us to do and forbade us from doing.

The verses about Li’aan are mentioned in Surat An-Noor (The Light) [Quran 24]

For Li’aan that you mentioned in your question, you may refer to Fatawa 193277, 428203, 122944, 176757, 200749, 88978, 90098 and 84301, about it.

Allah knows best.