It is reported about Sayyidah Aishah Siddiqah (may Allah be pleased with her) that once her mukatab slave (who had contracted to buy his freedom) came to her with the remaining amount of his contract. Sayyidah Aishah (may Allah be pleased with her) said to him: "After this time you will not be able to come in to me. You should take part in jihad in the way of Allah, for I heard the Prophet (peace and blessings be upon him) say: 'Whenever dust in the way of Allah enters the heart of a Muslim, Allah Almighty makes Hell forbidden for him.'"
Ahmad and al-Tabarani (in al-Mu'jam al-Awsat) recorded it. The narrators of Ahmad are thiqat (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجهاد / 9421