Is it permissible to supplicate with "O Allah, by the sanctity of Islam" or "by our love for your Prophet Muhammad, may Allah’s peace and blessings be upon him"? Is it also valid to supplicate with "O my master" or "O my lord" intending the Prophet or the imam of the mosque, or should one be restricted to [supplicating with] "O Allah" and "O Lord"?

It is permissible to make tawassul (supplication through an intermediary) to Allah by virtue of Islam, because it is a tawassul through a righteous deed and through the attributes Allah has ascribed to Himself out of His grace. Similarly, tawassul through love of the Prophet, peace and blessings be upon him, is permissible because it is one of the best deeds of the heart.

There is no harm in saying "O my Master" (Ya Sayyidi) or "O my Lord" (Ya Mawlay) with the intention of supplicating Allah, because "the Master" (As-Sayyid) is one of Allah's attributes, and Allah has described Himself as "the Protector of the believers" (Mawla al-Mu'mineen). It does not matter that these attributes are also applied to created beings, as long as the intention is to supplicate Allah through them.