Call upon your Lord in humility and privately; indeed, He does not like the transgressors.Qur'aan 7:55
Narrated Abu Musa Al-Ash`ari:
We were in the company of Allah's Messenger (sallallaahu alayhi wa sallam) (during Hajj). Whenever we went up a high place we used to say: "None has the right to be worshipped but Allah, and Allah is Greater," and our voices used to rise, so the Prophet (sallallaahu alayhi wa sallam) said, "O people! Be merciful to yourselves (i.e. don't raise your voice), for you are not calling a deaf or an absent one, but One Who is with you, no doubt He is All-Hearer, ever Near (to all things).
Sahih al-Bukhari Hadith No. 2992
Allah says says He does not like the transgressors. According to one view this transgression here refers to transgression in du'a.
Those who hold the opinion that transgression here means transgression in du'a, have three views as to what transgression in du'a means.
The first view is that it means to invoke du'a of evil against the believer like cursing him.
The second view is that it means that you make du'a for something which you do not have a right to make du'a for like asking Allah He gives you the ranks of the Prophets.
The third view is that it means to make du'a out loud.
زاد المسير في علم التفسير
Volume 2 Page 130