Uyayna bin Hisn came in to see the Messenger of Allah ﷺ and saw him kissing either Hasan or Husayn. He said to him, "Do not kiss him, Messenger of Allah. I have ten children, and I have never kissed any one of them."The Messenger of Allah ﷺ replied, "Whoever shows no mercy will be shown no mercy."
أخبرنا هشيم عن الزهري عن أبي سلمة
دخل عيينة بن حصن على رسول الله ﷺ فرآه يقبل حسنا أو حسينا فقال له لا تقبله يا رسول الله لقد ولد لي عشرة ما قبلت أحدا منهم فقال رسول الله ﷺ إن من لا يرحم لا يرحم
Its isnad is sahih. Abu Salama is the son of Abdul-Rahman bin Awf. The hadith was narrated by Bukhari 10:359-360 Fath, via Shuayb, and by Muslim 2:213, via Ibn Uyayna and via Maamar, and by Abu Dawud 4:524/5218 Awn al-Mabud, and by Tirmidhi 3:119, both of the latter two also via Ibn Uyayna. All three transmit it from Zuhri, with this isnad. But in all of their versions, it reads Aqra bin Habis instead of Uyayna bin Hisn. Likewise it will come in the Musnad at 7287, from the narration of Ibn Uyayna, and at 7636, from the narration of Maamar, and at 10684, from the narration of Muhammad bin Abu Hafsa, all three from Zuhri, with the same wording, giving Aqra bin Habis. Uyayna and Aqra were both among those whose hearts were won over, and both had ten children. But the report of four narrators, Shuayb, Ibn Uyayna, Maamar, and Ibn Abu Hafsa, is more reliable than this report in which Hushaym stands alone.He is a trustworthy and reliable memorizer of hadith, well known, but there is some discussion about his narration from Zuhri, in that he did not write down what he heard from him, or he wrote it on a sheet in Makkah, and the wind carried it off and cast it away, so they could not find it, and he retained only nine hadiths from it by memory. Perhaps this explains his error in this narration. It is remarkable that Ibn Hajar did not point out this narration of Hushaym, despite his rigorous scrutiny, precision, and eagerness to note differences among the various narrations.Regarding his saying, "Whoever does not show mercy will not be shown mercy," Ibn Hajar said in the Fath, both verbs are in the indicative mood, functioning as statements of fact. Iyad said this is the reading of the majority. Abu Baqa said, "man" (whoever) may be a relative pronoun, or it could be a conditional, in which case both verbs would be read in the jussive mood.A useful note, Qastallani erred in his commentary on Bukhari 9:14 when he claimed that this hadith is among those unique to Bukhari. In fact it is also found in Muslim, Abu Dawud, and Tirmidhi, as we have mentioned.