It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "Be sincere to one another in knowledge, for the betrayal by one of you in his knowledge is graver than his betrayal in his wealth, and Allah, the Mighty and Majestic, will surely question you about it on the Day of Resurrection."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11651