I once read in an Islamqa fatawa that cursing others will revoke your right to intercession if you are among the believers who were appointed to heaven. Is it true? If it is, then what are the hadiths that say so?
It seems Islam Q&A fatwa 21672 is the one being referred to here. They write:
It was narrated from the Prophet (peace and blessings of Allaah be upon him) that the intercession of some people will not be accepted on the Day of Resurrection, including those who cursed a great deal. Muslim narrated that Abu’l-Darda’ said: “I heard the Messenger of Allaah (peace and blessings of Allaah be upon him) say, ‘Those who curse will not be witnesses or intercessors on the Day of Resurrection.”
It seems to be referring to this hadith:
Zaid b. Aslam reported that 'Abd al-Malik b. Marwan sent some domestic goods for decoration to Umm Darda' on his own behalf, and when it was night 'Abd al-Malik got up and called for the servant. It seemed as if he (the servant) was late (in responding to his call), so he ('Abd al-Malik) invoked curse upon him, and when it was morning Umm Darda' said to him: I heard you cursing your servant during the night when you called him, and she said: I heard Abu Darda' as saying that Allah's Messenger (ﷺ) said: The invoker of curse would neither be intercessor nor witness on the Day of Resurrection. -- Sahih Muslim 2598 a (sunnah.com)