Allah says, some hypocrites bother the Messenger of Allah ﷺ by questioning his character, saying,
هُوَ أُذُنٌ
(he is (lending his) ear), to those who say anything about us; he believes whoever talks to him. Therefore, if we went to him and swore, he would believe us. Similar was reported from Ibn `Abbas, Mujahid and Qatadah. Allah said,
قُلْ أُذُنُ خَيْرٍ لَّكُمْ
(Say: "He listens to what is best for you"), he knows who's saying the truth and who is lying,
يُؤْمِنُ بِاللَّهِ وَيُؤْمِنُ لِلْمُؤْمِنِينَ
(he believes in Allah; has faith in the believers), he believes the believers,
وَرَحْمَةٌ لِّلَّذِينَ ءَامَنُواْ مِنكُمْ
(and is a mercy to those of you who believe"), and a proof against the disbelievers,
وَالَّذِينَ يُؤْذُونَ رَسُولَ اللَّهِ لَهُمْ عَذَابٌ أَلِيمٌ
(But those who annoy Allah's Messenger, will have a painful torment.)