if you missed fajr salaah and you only remembered after reading zuhr salaah, will ur zuhr salaah be accepted. if you happen to be imaam for the zuhr salaah do the musalees need to repeat salaah

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

If a person forgets a prayer and he does not remember it until he has performed another obligatory prayer, then he is not sinful as the Prophet said: ''Allaah has forgiven my nation for things they forget, or do by mistake, or which they are forced to do.'' [Ibn Maajah] Besides, Allaah The Almighty Says (what means): {"Our Lord, Do not impose blame upon us if we have forgotten or erred.} [Quran 2:286] In response to this, Allaah said: “Indeed, I did.” [Muslim]

However, you are obliged to make up the prayer that you forgot to perform, as the Prophet said: ''Whoever forgets a prayer should perform it as soon as he remembers it; there is no (other) expiation for it except that (i.e. to pray it as soon as one remembers it." Then the Prophet recited the verse in which Allaah The Almighty Says (what means): {…and establish prayer for My remembrance.} [Quran 20:14] [Al-Bukhari and Muslim]

For more benefit, please refer to Fataawa 113054, 90052, 89978 and 85950.

Therefore, if you forgot to pray the Fajr prayer until after praying Thuhr, then you are only required to pray the Fajr prayer and you do not repeat the Thuhr prayer. You are not considered sinful and your prayer as well as that of the people whom you led in prayer is valid.

Allaah Knows best.