God says:

And establish regular prayer for My remembrance. (Ta-Ha 20:14)

‘My remembrance’ is said to have an active sense: ‘In order that I (God) might remember you thereby’. It is also said to refer to the One remembered: ‘That you might remember Me thereby’, with the letter lam (L, in li-dhikrii ‘for My remembrance’) in both cases expressing purpose.

Others, however, argue that the lam carries a sense of time:

Establish the prayer when I am mentioned”, as in the verse:

Establish the prayer at the sun’s setting… (Al-Israa’ 17:78)

Or the verse:

And We all set up the scales with justice on the Day of Judgment… (Al-Anbiyaa’ 21:47)

In these two verses, time is certainly meant, but in the present case this explanation is merely an opinion. The difference is that in the latter two verses, the lam of time precedes the nouns of time ‘the Sun’s setting’ and ‘the Day of Judgment’; whereas in the first verse, it precedes a noun ‘My remembrance’ derived from a verb, unless we agree that an expression of time is understood, so that the verse means ‘at the time of My remembrance’, which is possible.

However, lam most plainly expresses purpose. The verse means ‘Establish the prayer for the sake of My remembrance’. This includes the fact that the prayer is offered at the time that God is remembered; and the fact that when the servant remembers his Lord, God’s remembrance of him has preceded his remembrance of God. For when God remembers His servant, it inspires the servant to remember Him. Therefore, all three meanings are correct.

God has also said:

Recite what has been revealed to you of the Book and establish the prayer. Verily, the prayer restrains from shameful and unjust deeds. And God’s remembrance is greater. (Al-`Ankabut 29:45)