What is the ruling of Islamic law regarding a landlord reducing the rent for those who pay within the first five days, and gradually increasing it for those who delay payment?

If the rent is fifty thousand, and the owner reduces it to forty thousand for whoever pays within the first five days, and to forty-five thousand for whoever pays after ten days, there is no harm in that. This is considered a conditional gift, encouraging early payment. The conditioning of a gift upon a condition is permissible according to some Hanafis and Hanbalis, and it was chosen by Ibn Taymiyyah and Ibn al-Qayyim, who cited the hadith of Jabir and some other hadiths from which its permissibility can be understood.