once
أَحَبَّكَ الَّذِي أَحْبَبْتَنِي لَهُ
Edition transliteration
Ahabbakal-lathee ahbabtanee lah.
Meaning
May He, for whom you have loved me, love you.
Source and references
Hisn al-Muslim, entry 200.The reference is copied from the edition; separate editorial verification is not complete yet.
Source edition: Fortress of the Muslim. Open source ↗