Source: Tafsir al-Ahlam al-Kabir (Ibn Sirin)
Whispering in a dream indicates hidden speech or cunning. Whoever sees himself whisper in someone's ear is revealing a secret to him.
Source: Ta'tir al-Anam fi Ta'bir al-Manam (Al-Nabulsi)
Whispering indicates backbiting and gossip. Whoever sees people whispering are plotting against him.
Source: Al-Isharat fi Ilm al-Ibarat (Ibn Shahin)
Whispering is interpreted as worry. Whoever sees himself whisper is in worry.