ALIF LAM MIM. The Arabic letters الم, corresponding to A. L. M. which occur at the commencement of six Surahs, namely Su’ratu ‘l-Baqarah (ii), Suratu ‘Ali ‘Imran (iii.), Suratu ‘l-’Ankabut (xxix.), Suratu ‘t-Rum (xxx.), Suratu Luqman (xxxi), and Suratu ‘s-Sijdah (xxxii.). Muhammad never explained the meaning of these mysterious letters, and consequently they are a fruitful scarce of perplexity to learned commentators. Jalalu ‘d-din gives an exhaustive summary of the different views in his Itqan (p. 470). Some suppose they stand for the words Allah “God”; Latif, “gracious”; Majid, “glorious.” Others say they stand for Ana ‘llu a’lamu, “I am the God who knoweth.” Others maintain that they were not meant to be understood, and that they were inserted by the Divine command without explanation in order to remind the reader that there were mysteries which his intellect would never fathom.
Based on Hughes, Dictionary of Islam