The Quran

وَمِنهُمُ الَّذينَ يُؤذونَ النَّبِيَّ وَيَقولونَ هُوَ أُذُنٌ ۚ قُل أُذُنُ خَيرٍ لَكُم يُؤمِنُ بِاللَّهِ وَيُؤمِنُ لِلمُؤمِنينَ وَرَحمَةٌ لِلَّذينَ آمَنوا مِنكُم ۚ وَالَّذينَ يُؤذونَ رَسولَ اللَّهِ لَهُم عَذابٌ أَليمٌ

Muhammad Asad

AND AMONG those [enemies of the truth] there are such as malign the Prophet by saying, "He is all ear."¹ Say: "[Yes,] he is all ear, [listening] to what is good for you!² He believes in God, and trusts the believers, and is [a manifestation of God's] grace towards such of you as have [truly] attained to faith. And as for those who malign God's Apostle - grievous suffering awaits them [in the life to come]!"

I.e., "he believes everything that he hears". Most of the commentators assume that the hypocrites were thus alluding to the Prophet's alleged propensity to believe everything - good or bad - that he was told about other people (cf. Manar X, 600). Since, however, there is no historical evidence of such a "propensity" on his part, it seems to me that what the hypocrites referred to was the Prophet's readiness to listen to what they - in common with many other unbelievers regarded as mere hallucinatory sounds, and to interpret them "mistakenly" as revelations. This would explain the statement that "they malign the Prophet" - namely, by attributing to him self-deception - and that this saying of theirs "amounts to a denial of the truth" (see verse 74 of this surah).- The verb adha signifies primarily "he molested" or "annoyed [another]", i.e., in a manner not amounting to actual harm (darar). Since in the above context this verb is used in the sense of making a derogatory remark, yu'dhun is best rendered as "they malign".
I.e., to divine revelation.