Is it permissible to write: “Allahumma salli 'ala Muhammad” (اللهم صلي على محمد) or is the correct way to write it: “Allahumma salli 'ala Muhammad” (اللهم صل على محمد)?

Writing "صلي" (salli) with a yaa’ (ي) in the phrase "اللهم صل على محمد" (Allahumma salli 'ala Muhammad - O Allah, send blessings upon Muhammad) is incorrect. This is because "صَلِّ" (salli) is an imperative verb built on the omission of the weak letter (harf al-illah), whereas "صلي" (salli) with a yaa’ is an imperative for a female, and the yaa’ in it is the yaa’ of the doer (yaa’ al-faa'ilah), similar to the Almighty’s saying: (So eat and drink and be content).