"Sa'd was wounded on the day of Al-Khandaq when a man of Quraish shot him in the medial arm vein. The Messenger of Allah (ﷺ) pitched a tent (Khaimah) for him in the Masjid so that he could visit him close at hand."

Al-Khandaq means the trench. This indicates the battle of the trench which took place during the fifth year after Hijrah.
Sunan an-Nasa'i Book 8, Hadith 23
← Previous Hadith "When the Messenger of Allah (ﷺ) wanted to observe I'tikaf, he would pray Fajr then enter the place where he wnated to observe I'tikaf. He wanted to observe I'tikaf during the last ten days of Ramadan, so he commanded that a Khiba' (tent) be pitched for him. Then Hafsah ordered that a Khiba' be pitched for her, and when Zainab saw her tent she ordered that a Khiba' be pitched for her too. When the Messenger of Allah (ﷺ) saw that he said: 'Is it righteousness that you seek?' And he did not observe I'tikaf in Ramadan, and observed I'tikaf for ten days in Shawwal (instead)."

Al-Khiba': "One of the house of the Bedouins made of Wabir (camel or goat fur) or wool, not of hair (from other pelts). And it would have two or three posts." (An-Nihayah)

Seclusion in the Masjid for the sake of devotion to Allah.

Sunan an-Nasa'i Book 8, Hadith 22 Next Hadith → "While we were sitting in the Masjid. The Messenger of Allah (ﷺ) came out to us carrying Umamah bint Abi Al-'As bin Ar-Rabi', whose mother was Zainab, the daughter of the Messenger of Allah (ﷺ). She was a little girl and he was carrying her. The Messenger of Allah (ﷺ) prayed with her on his shoulder, putting her down when he bowed and picking her up again when he stood up, until he completed his prayer."

Sunan an-Nasa'i Book 8, Hadith 24