When two persons indulge in hurling (abuses) upon one another, it would be the first one who would be the sinner so long as the oppressed does not transgress the limits. (Using translation from Muslim 2587)
أَنَّ رَسُولَ اللهِ ﷺ قَالَ الْمُسْتَبَّانِ مَاقَالَا عَلَى الْبَادِئِ مَا لَمْ يَعْتَدِ الْمَظْلُومُ وَالْمُسْتَبَّانِ شَيْطَانَانِ يَتَكَاذَبَانِ وَيَتَهَاتَرَانِ